
Class (^ /£>/ 

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CjQEffilGHT DEPOSIT 



SCIENCE 
FOR BEGINNERS 



BY 
FREDERIC DELOS flARBER, A.M., 

Professor of Physics, Illinois State Normal University 

MERTON LEONARD FULLER, M.Di., M.A., 

Meteorologist. U. S. Weather Bureau; Lecturer on Meteorology*. 
Bradley Polytechnic Institute 

JOHN LOSSEN PRICER, A.M., 

Late Professor of Biology, Illinois State Normal University 
AND 

HOWARD WILLIAM ADAMS, B.S., 

Professor of Chemistry, Illinois State Normal University 




NEW YORK 

HENRY HOLT AND COMPANY 

1921 






Copyright, 1921, 

BY 

HENRY HOLT AND COMPANY 



DEC 21 71 



©B.A630910 



**>c 



PREFACE 

This book is in effect a simplification, for younger pupils, 
of the authors' "First Course in General Science." There 
are fewer quantitative conceptions, many mathematical 
problems have been eliminated, and, where it has been pos- 
sible without sacrificing clearness, much detail has been 
omitted. The chapters on Weather and Microorganisms 
have been made far less technical. The logical and seasonal 
order of topics has been improved by following the discus- 
sion of Foods with the chapter on Refrigeration and preced- 
ing it with the treatment of Microorganisms. In fact, the 
whole treatment has been so largely rewritten that it may 
fairly be regarded as a new book. It discusses, in terms that 
the youthful mind can understand, phenomena of science con- 
stantly met in the home, the school, and the community. It 
arouses the pupil's curiosity about them and sets him to find- 
ing the explanation of them. Each topic is pursued far 
enough to avoid superficiality and to give continuity to the 
course. The course is progressive; the earlier chapters are 
relatively easy; as the ability of the pupil grows, the course 
becomes correspondingly difficult. Numerous cross refer- 
ences are given to stimulate frequent reviews. Topics not es- 
sentially important in the environment of any class, or in the 
environment of the community, msCy easily be omitted with- 
out seriously breaking the continuity of the course. 

Like its predecessor this book assumes that the first year 
of science instruction should not aim primarily to survey the 
entire field of nature and present scattered bits and choice 
morsels from every special science in order that the pupil 
may decide in which of the sciences he would like to special- 

iii 



iv PREFACE 

ize further. Nor is first-year science regarded as only 
an introduction to the special sciences. It has been shown to 
have a vastly more important function to perform, namely to 
give a rational, orderly, scientific understanding of the pu- 
pil's environment to the end that he may correctly interpret 
it. General science has justified itself by its own intrinsic 
value as a training for life's work. 

We wish to express our appreciation of the aid rendered 
by those who have assisted in the preparation of the illustra- 
tions or who have granted us permission to use illustra- 
tions from their publications. The hearty cooperation of 
manufacturers and business men and the interest they have 
manifested in our efforts to present faithfully the applica- 
tion of science to the actual affairs of life have been most 
helpful. The authors wish to make particular acknowledg- 
ment of assistance from the following sources : The Century 
Company, Figs. 1, 59, 78, 303, 306, 311. Detroit Heating & 
Lighting Company, Figs. 15, 16. Westinghouse, Church, 
Kerr & Co., Figs. 35, 36. American Home Magazine Co., 
Figs. 37, 38, 39. General Electric Co., Figs. 40, 41. Central 
Electric Co., Figs. 31, 32, 44, 46, 47, 48. Welsbach Company, 
Figs. 50, 51, 52, 53. Curtis Publishing Co., Fig. 60. Kala- 
mazoo Stove Co., Figs. 67, 99. Patric Furnace Co., Figs. 68, 
69. Williamson Heating and Ventilating Co., Figs. 70, 71, 
72, 83, 84, 85. American Radiator Co., Figs. 184, 185. Dur- 
ham Manufacturing Co., Fig. 100. Mechanical Refrigerator 
Co., Fig. 224. Monthly Weather Review, Figs. 113, 115, 117, 
132, 141, 153, 156, 157. Dr. S. Adolphus Knopf and Moffat, 
Yard & Co., Fig. 181. Hoover Suction Sweeper Co., Fig. 187. 
Municipal Journal, Fig. 188. Standard Sanitary Manufac- 
turing Co., Figs. 239, 246, 260, 261. R, D. Wood & Co., Figs. 
245, 249. Bishop & Babcock Company, Fig. 249. Rens- 
selaer Manufacturing Co., Fig. 251. National Meter Co., 
Figs. 254, 255. International Harvester Co., Figs. 275, 
314, 316, 318, 320. Singer Sewing Machine Co., Figs. 276, 277, 



PREFACE V 

278, 279, 280, 281, 282. Mississippi Power Co., Figs. 296, 297, 
302. DeLaval Manufacturing Co., Figs. 283, 284, 285. 
American Book Co., Fig. 304. James Leffel & Co., Figs. 309, 
310. Westinghouse Manufacturing Co., Fig. 54. Swift & Co., 
Figs. 212, 213, 214. Creamery Package Co., Fig. 211. United 
States Weather Bureau, Figs. 118, 119, 123, 124, 125, 134, 140, 
142, 143, 144, 145, 154. Hersey Manufacturing Co., Fig. 253. 
Pearse, Greeley, and Hansen, Figs. 271, 272, 274. Erie Rail- 
road Company, Fig. 291. John Wiley & Sons, Fig. 273. 
Some of the illustrations appear unmodified ; some have been 
adapted to their present use; others have been prepared es- 
pecially for the book. 

The Authors 
Normal, Illinois, 
September, 1921. 



CONTENTS 

CHAPTER PAGE 

I The Production and Use of Light 1 

1. Primitive Lighting — 2. The Kerosene Lamp — 3. Evap- 
oration, Boiling Temperature, and Distillation — 4. Petro- 
leum and Its Products — 5. Properties of Gasoline — Sources 
of Danger: Density; Flashing Point and Burning Point — 
6. The Gasoline Gas Machine — 7. Manufactured Gasoline, 
•and Motor Spirit — 8. Our Supply of Petroleum — 9. Illu- 
minating Gas Lighting: Gas Meter; Reading a Meter; 
Pressure of Gas — 10. Electric Lighting: Incandescent and 
Nitrogen Lamps; Electric Wiring — 11. Natural and Artifi- 
cial Lighting: Importance of Studying the Lighting Ques- 
tion; Direct and Diffused Light; Relative Cost of Opera- 
ting Gas and Electric Lights. 

II The Production and Use of Heat 66 

1. The Beginning of Warmth and Comfort: Importance of 
Fire; Early Stoves — 2. The Chemistry of Fire: Chemical 
Elements; Chemical Union; Fuel Elements — 3. Smoke; 
Its Cause and Prevention ; Construction of Stoves to 
Prevent Smoke — 4. Liquid Fuels — 5. Gaseous Fuels: Coal, 
Water and Gasoline Gas — 6. Our Coal Supply : Develop- 
ment of Coal Production ; Waste in Mining ; How Long 
Will Our Coal Supply Last; Coal Fields of the United 
States — 7. Development of House Heating: Ancient 
Methods; Invention of the Chimney; Convection Currents; 
Application of Convection Currents to Chimneys; Setting 
of Furnaces; Hot Water. Heating; Steam Heating — 8. 
Development of Cooking Devices; Coal and Wood Cook 
Stoves; Gas Range; Fireless Cooker. 

III The Weather 133 

1. Methods of Studying the Weather— 2. The Use of Wea- 
ther Instruments: Barometer; Barograph; Thermometer; 
Thermograph — 3. The Atmosphere and Its Temperature — 
4. The Water Vapor of the Air : Clouds, Fog, Rain, Snow, 

vii 



Viii CONTENTS 

CHAPTER PAGE 

Dew and Frost; Measuring the Water Vapor— »5. Local 
Storms: Showers; Thunderstorm; Tornado — 6. The Gen- 
eral Storm; A Low Pressure Area: Weather Map; Pres- 
sure Areas in General ; General Circulation of the Atmos- 
phere; Effects of the Sun's Annual Migration. 

IV The Seasons — Climate and Health .... 209 

1. The Sun — The Cause of the Seasons — 2. Climate and 
Life: Plant Life and Animal Life Determined by Climate 
Man's Relation to Climate — 3. The Factors Which Deter- 
mine Climate: Temperature; W T inds; Sunshine — 4. Cli- 
matic Regions of the United States — 5. Protection Against 
Unfavorable Climate. 

V Ventilation 233 

1. Principles of Ventilation: Need of Ventilation; Amount 
of Fresh Air Needed per Minute by Each Person ; Relation 
of Humidity to Ventilation ; Effect of Air Movement ; 
Importance of Proper Humidity; Large Amounts of Water 
Must Be Evaporated; Humidifying the Air of School- 
rooms — 2. Systems of Ventilation: Modern, Natural or 
Gravity System and Forced System : Thermostat Control 
of Temperature; Suction System of Heating and Ventila- 
tion — 3. Dust and Its Dangers: Live Dust and Dead Dust; 
House Dust; Vacuum Cleaning. 

VI Micro-organisms — Their Relation to Our Food 

Supply, to the Soil, and to Our Health . . 260 

1. Saprophytes — Plants Which Live Upon Dead Organic 
Matter: Molds; Yeasts; Bacteria Soil; Conditions Which 
Favor Bacterial Growth; Antiseptics; Disinfectants; Pres- 
ervation of Food by Canning; Sterilization and Pasteur- 
ization — 2. Parasites — Organisms Which Live Within the 
Bodies of Other Living Organisms: Anthrax; Smallpox; 
Diphtheria; Other Bacterial Diseases; Important Facts 
About Common Diseases: Typhoid; Influenza; Common 
Colds; Tuberculosis — 3. Public Health. 

VII Food 322 

1. The Diet: What Substances Must the Foods Furnish to 
the Body; What Is Food? The Food Principles: Fats, Car- 
bohydrates, Proteins; Heat Value of the Food Principles— 

2. Processing Food; Dairy Products; Preserving Meat: 






CONTENTS ix 

APTEB PAGE 

by Cold Storage, by Use of Salt and Other Chemicals; 
Meat Inspection ; the Cereal Foods ; Sugar : Cane, Beet. 

VIII Refrigeration and Its Uses 358 

1. The Refrigerator, Principle, Construction and Styles 
of — 2. Manufactured Ice and Freezing Mixtures: the Ice 
Plant; Purity and Cost of Manufactured Ice — 3. Cold 
Storage: Construction of Plant; Refrigeration and Trans- 
portaticn. 

IX Ground- Water and Ground- Air 381 

1. Ground-Water: Rainfall; Visible and Invisible Water 
Supply; the Water Table — 2. Ground-Air: Movements of 
Soil-Air ; Soil Temperatures — 3. Conservation of Soil Mois- 
ture — 4. Relation of Ground- Water to Wells; Surface and 
Deep Wells. 

X Water Supply and Sewage Disposal . . . 404 

1. The Value of Water — 2. Water Supply for Farm-House 
and Country Home: Well-Sweep; Pumps: Suction, Lift 

and Force — 3. City Water Systems: Sources of Supply; 
Development of System; Water Pressure; Fire Hydrant; 
Water Meter — 4. Sanitary Plumbing — 5. Disposal of Sew- 
age: City; Country; "By Dilution", "Broad Irrigation 

by Sewage"; Septic Tanks and Filter Beds; Activated 
Sludge Methcd. 

XI Machines, Work and Energy ..... 452 

1. Machinery in the Home and on the Farm — 2. Some 
Common Machines: The Sewing Machine; Cream Separa- 
tor — 3. Mass, Weight, Force. Work, and Power — 4. 
Machines and Their Uses — 5. Energy and Its Relation to 
the Use of Machines — 6. Some Common Mechanical 
Motors: Water Motors; Available Water Power of the 
United States; The Steam Engine; The Gas Engine; Gas- 
oline Motors and Aeroplanes. 



SCIENCE 
FOR BEGINNERS 



CHAPTER I 

THE PRODUCTION AND USE OF LIGHT 

I. PRIMITIVE LIGHTING 

i. The Discovery of Fire. — There probably was a time 
when primitive man was without fire. In those days he had 
no artificial heat or light, and he 
ate his food uncooked. Perhaps 
man first obtained fire from dead 
trees ignited by lightning, per- 
haps from oil wells which are 
known to have been burning for 
centuries. With fire came 
warmth, light, and cooked food. 
The light from the camp fire also 
furnished protection from wild 
animals. Gradually the fire came 
to be the center of the home. It 
is probable that we owe more than 
we realize to fire for what it has 
done toward building up and 
strengthening home ties. 

2. The Primitive Lamp. — Per- 
haps a pine knot snatched from 
the fire constituted the first portable light. How re- 
cently pine knots have been in common use is shown by the 

1 




Fig. 1. — A Roman lamp. 
From Stories of Useful Inven- 
tions. ( By courtesy of The 
Century Company.) 



2 THE PRODUCTION AND USE OF LIGHT 

fact that Abraham Lincoln learned to read by the light of 
them. Perhaps by collecting the grease obtained from cook- 
ing and placing it in a rude vessel with a bit of bark or a 
thread of twisted moss for a wick, man made the first lamp. 
We would consider the light produced by such a lamp a poor 
one indeed, but the Eskimos still use such primitive lamps. 
The bowl is hollowed out from soapstone ; the fat comes from 
the animals they slay. The Eskimo lamp serves also as a 
stove. By its heat all their cooking is done and their snow 
huts are warmed. 

3. Greek and Roman Lamps. — The lamps of Greece and 
Rome were no better than the Eskimo lamps of today, but 
the lamp bowls were often very costly and elaborately orna- 
mented (Fig. 1). The rich used lamps of bronze or silver; 
the middle classes, lamps made of terra-cotta ; the poor, cheap 
iron lamps. 

4. The Early Candle. — The earliest lamps could not con- 
veniently be moved about. The oil or fat, especially when 
warm, spilled out of the bowl. It was noticed, probably, that 
when some fats were cold they became quite stiff and solid. 
Tallow is much more solid than lard. Someone concluded, 
therefore, that it would not be necessary to use a lamp bowl at 
all if tallow were used and a small wick imbedded in it. The 
tallow prepares its own bowl during the process of burning. 
Like lamps, candles have been used from prehistoric times. 

5. Modern Candles. — While the candles our grandfathers 
and grandmothers made were of tallow, the modern candle is 
made of paraffin which is obtained from petroleum. Over 
300,000,000 paraffin candles are sold in the United States 
each year, about two dozen candles for each family. 

Exercise 1. — How the Candle Burns 

Place a piece of candle upright on a square of pasteboard after 
melting a little of the paraffin at the bottom of the candle to make 
it stick. Light the candle. After it has burned three or four min- 
utes notice what is happening to the paraffin near the wick. This 






PRIMITIVE LIGHTING 3 

cup corresponds to the bowl of the primitive lamp. To have a 
perfect cup three things are necessary : (1) There must be no draft 
in the room; (2) the wick must not be too large for the candle; 
(3) the wick must be in the center of the candle. Is it desirable to 
have the cup perfect? Why? 

Hold one of the strands of candle wicking in a vertical position 
and light its upper end. Does it burn readily? Does it continue 
to burn? Is its flame like that of the candle flame? Is it the 
burning of the candle wick that is the chief cause of the candle 
flame? If not, what is it? 

Blow out the candle flame and examine the wick. Is it wet? 
With what is it wet ? Does it remain wet all the time that the candle 
is burning? Re-light the candle and, using two iron nails, squeeze 
the wick; then examine the nails to see whether or not 
there is any paraffin on them. The wick is constantly 
soaked in melted paraffin while the candle burns. 
But is it the liquid paraffin which burns? 

Re-light the candle and blow out the flame again. 
Notice the smoke which rises from the wick. How 
long does it continue to rise? Re-light the candle. 
Hold the lighted match in one hand. Blow out the 
caudle and quickly thrust the lighted match into the 
?olumn of rising smoke about 1 in. above the candle. 
What happens? (Fig. 2.) Try the same again. Fig. 2.— 

Make several trials to see how far above the tip of Lighting the 
the wick you can hold the match and still have the an eva P 01 - 
candle re-light. Does it make any difference how 
long you wait after blowing out the flame before applying 
the match? Do drafts through the room make a difference? What 
do you now think it is that burns? 

Have you ever seen a frying pan in which bacon or eggs 
were frying become so hot that the smoke rising from the fat 
caught on fire? This sometimes happens. The fat, how- 
ever, begins to smoke some time before it gets hot enough 
to catch on fire. 

The Explanation. — All kinds of greases, fats, and oils when 
heated sufficiently hot give off vapors in large quantities. 
This simply means that these fats and oils are changed o\J 
heat from liquids into vapors, or gases, exactly as water is 




4 THE PRODUCTION AND USE OF LIGHT 

changed by heat from its form as liquid water into steam , or 
water vapor. It is paraffin vapor which burns in the candle 
flame. 



Exercise 2. — The Flashing Point and the Burning Point 

Put a little paraffin in a large spoon and slowly 
heat it until it begins to smoke, vaporize (Fig. 3). 
Then test the smoke, vapor, frequently with a burn- 
ing match to see when it will ignite. At a certain 
temperature of the liquid paraffin in the spoon the 
vapor becomes dense enough to produce a momen- 
tary flash over the surface. The paraffin is then 
at the flashing point. Continue to heat the paraf- 
fin in the spoon slowly, testing the vapor as before. 
riG.3— Flash- When the vapor becomes dense enough to burn 
naraffin continuously, the paraffin has reached the burning 

point. 

Definitions. — The flashing point of paraffin, lard, tallow, 
or oil is that temperature at which the vapor arising and mix- 
ing with air produces a momentary flash when ignited. 

The burning point is that temperature of the substayxce at 
which the vapor arising and mixing with air produces a con- 
tinuous flame when once ignited. 

It is now evident that in lighting a candle the burning 
match must be held against the wick long enough 
to melt and then to vaporize the paraffin in it in 
such quantities that the vapor is ignited by the 
match and burns with a continuous flame. The 
heat from the candle flame continues to melt and 
to vaporize the paraffin fast enough to produce eluding fresh 
a steady flame. air from the 

6. Fresh Air is Necessary. — We have seen 
that the vapor from the heated tallow or paraffin rises and 
mixes with the air. Is the air really necessary that the vapor 
may burn? We can answer the question best by trying an 
experiment. 



THE KEROSENE LAMP 5 

Exercise 3. — Shutting the Fresh Air Away from the Candle 

Light a piece of candle 1 or 2 in. in length and stand it on the 
table before you. Watch it for a minute to see that it burns prop- 
erly. Now invert a tumbler and place it over the candle. Does the 
candle continue to burn? Remove the tumbler. Re-light the candle. 
Try the experiment again, using a 2-qt. fruit jar instead of the 
tumbler. Does the candle continue to burn longer this time? "Why? 
Re-light the candle. Again place the fruit jar over the burning 
candle. Watch carefully to see what happens just as the flame 
goes out. Is there much smoke given off for a moment after the 
flame dies out? What is this smoke? If it is paraffin vapor, why 
does it not burn? (Fig. 4.) 

Now carefully raise the jar and set it aside while you re-light the 
candle, letting just as little fresh air into it as possible. Again 
place the jar over the candle and notice carefully how long the 
flame continues this time. Raise the jar, blow all the smoke out 
of it; re-light the candle and again place the jar over the candle. 
Does the flame burn longer than it did before? Explain. 

Explanation. — As long as the wick is hot there will be 
plenty of paraffin vapor. But this vapor cannot burn alone. 
The flame is the result of the uniting of the vapor with one of 
the gases, oxygen, in the fresh air. The air is not fresh when 
the vapor has burned out the oxygen. No matter how much 
of the burned air and vapor you may have in the tumbler, 
or how well mixed they may be, you can not get a flame till 
you have some of the fresh, unburnt air mixed with the vapor. 



II. THE KEROSENE LAMP 

7. The First Kerosene Lamp. — The kerosene lamp has been 
in use only about 60 years. The lamps which had previously 
been used usually burned heavy oils and fats, which gave only 
low, flickering, smoky flames. During the first half of the last 
century whale oil was in common use along the seacoast. 
Whale oil lamps were less smoky and disagreeable than most 
lamps of the period. A few lamps had been made which 



THE PRODUCTION AND USE OF LIGHT 



burned so-called burning fluids. But these fluids were very 
inflammable and dangerous. Up to about 1860 candles were 
by far the safest and best sources of 
artificial light which the world had 
ever used. 

It was in August, 1858, that the first 
successful oil well was sunk in Penn- 
sylvania. Petroleum had been known 
for a long time, but it had never before 
been found in commercial quantities 
and little use had been made of it 
except as medicine. Soon after it was 
obtained in large quantities, the dis- 
covery was made that an oil could be 
obtained from crude petroleum which 
would burn freely and still be safe to 
handle. This new oil was called kero- 
sene, though some people, supposing 
that it came from coal, called it coal 
oil. We still sometimes hear it called 
by that name. Inventors soon made 
lamps well suited for the burning of 
this oil. The common kerosene lamp 
of today is, in principle, exactly like 
those earliest lamps. 

8. Parts of the Kerosene Lamp. — 
The ordinary kerosene lamp really consists of three parts: 
(1) The bowl for containing the oils ; (2) the wick ; (3) the 
burner and chimney- The wick is usually made of soft, 
loosely woven cotton cloth. What is its purpose ? What does 
it do? 

Burners vary much in construction, but all have certain 
necessary parts, namely: (1) The cap, or crown ; (2) the 

PERFORATED BASE; (3) the TUBE FOR THE WICK. 




Fig. 5. — Parts of the 
burner. 



THE KEROSEXE LAMP 7 

Exercise 4. — The Use of the Burner and Chimney 

Examine a burner carefully and discover these parts. Make a 
sketch in your notebook of your burner showing clearly each of these 
parts. Label all parts of your sketch somewhat as the sketch, Fig. 
5, is labeled. Do not copy the sketch from the book but sketch your 
lamp. 

Study carefully the device for regulating the height of the wick. 

Light the lamp, place the chimney in position, and observe the 
steadiness of the flame. If there is not much draft through the room 
there should be very little flickering of the flame. It should burn 
with a steady flame. 

"Wave your book past the bowl of the lamp so as to produce a 
strong gust of air against the under side of the burner. "What is the 
effect upon the flame? Can you tell why it becomes smoky? Did 
you increase or decrease the amount of air which was passing 
through the chimney and past the flame? Hold the 
lamp up before you and blow strongly into the bottom 
of the burner. What is the effect upon the flame? Is 
it a case of too much air or not enough? 

Wrap a towel about the base of the burner to prevent 
air from entering through the perforated base. What 
is the effect upon the flame? If you could see only the 
upper portions of the chimney could you be certain 
from the behavior of the flame whether too much or too Fig. C. 

little air was entering the burner? Burning 

Place a piece of cardboard or window glass for an Kerosene 
instant on •the top of the chimney so as to close it. What burner, 
is the result ? What is the effect upon the flame of hav- 
ing too little air? What is the effect of having too much air? 
What do you think is the chief purpose of the burner and chimney? 

Kerosene burns just as freely without the use of a burner 
or chimney. This can be easily shown by placing some kero- 
sene in a tumbler and covering the tumbler with a sheet of tin 
in which a slit has been cut by means of a cold chisel. An 
ordinary lamp wick is drawn into the slit as shown in Fig. 6. 
In this case, however, the flame will be smoky and unsteady 
no matter how still the air in the room may be. 

Evidently, the chief purpose of the burner and chimney is 




THE PRODUCTION AND USE OF LIGHT 



to regulate the air supply. If the air supply he either too 
abundant or too scarce the flame will be unsteady and smoky. 
We shall see later why this is so. We shall also study later 
the principle by which the burner and chimney regulate the 
air supply. 

9. How Kerosene Burns. — Just as we proved that it was 
not the liquid paraffin which burned in the case of the candle, 
so we can show that it is not the liquid kerosene which burns 
in the case of the kerosene lamp. 

Exercise 5. — It is Kerosene Vapor that Burns 

Remove the chimney from the lamp. Light it. Hold the lighted 
match ready to apply. Blow out the flame. Quickly apply the 
lighted match to the rising column of smoke. 
Does it ignite? If not, be quicker in applying 
the match next time. Repeat the experiment 
to see how far above the wick you are able to 
ignite the vapor. 

Have you ever noticed a strong odor of 
kerosene in the room after "blowing 
out" a lamp? (Art. 86.) Explain. 
Can this be prevented by first turning 
the wick down so as to produce a low 
flame before blowing it out? Ex- 
plain. 

10. Center Draft Burners. — Many 
large kerosene lamps use circular wicks. 
They have an open tube extending from 
the top of the burner down through the 
center of the bowl to the open central 
portion of the base. The rim of the base 
is perforated so that a current of fresh 
air can readily pass upward through the 
tube to supply the inside of the flame. 
There are, of course, perforations through 
the sides and bottom of the burner to supply fresh air to the 




/£>£)■ QQ&Q\ 



Fig. 7. — Center-draft 
lamp. 



EVAPORATION, BOILING TEMPERATURE, ETC. 9 

outside of the flame. Such lamps are known as center draft 
lamp*. (Fig. 7.) 

III. EVAPORATION, BOILING TEMPERATURE, AND 
DISTILLATION 

Evaporation 

ii. Need of New Terms. — We have thus far been studying 
the burning of paraffin in the candle and of kerosene in the 
ordinary lamp. Gasoline has often been used for producing 
artificial light where gas or electricity is unobtainable. Gaso- 
line lamps of many different kinds have been made and in 
many homes gasoline is used both for lighting and cooking. 
With this increase in its use people have discovered that gaso- 
line is also one of man's most dangerous servants if not care- 
fully and properly handled. Many accidents have resulted 
from its use. Most people who use gasoline know that it is 
more dangerous than is kerosene. But many people are using 
gasoline every day who do not know just why it is dangerous, 
what to do with it, or how to handle it to make it a safe and 
obedient servant. 

We should like to study gasoline; we hope to learn its 
nature and how to handle it. Before we can do so, how r ever, 
we must know the meaning of certain terms and how to use 
them correctly. We must know where gasoline comes from 
and its relation to kerosene. These topics w T ill be studied next. 

12. Evaporation. — We are all aware that damp clothes hung 
upon the line at any time except when it is raining soon lose 
the water they contain and become dry. We wash our porches 
and floors and soon they are dry. We place a basin of 
water in an exposed place and the water soon disappears. 

The explanation is that the water changes from a liquid to 
a gas, or vapor, and escapes into the air. This process by 
which water changes from its liquid form into a gas, or 
vapor, we call evaporation. 

The washerwoman also knows that on some days the clothes 



10 THE PRODUCTION AND USE OF LIGHT 

will dry much more rapidly than on others. We know that 
the freshly washed floors will dry more quickly if we open the 
doors and windows or build a fire in the furnace or stove. 
The farmer has learned to tell very accurately, by watching 
the weather, whether or not the fields and roads are drying 
rapidly. The question arises : What are the conditions under 
which evaporation takes place most rapidly? This question 
can best be answered by experiment. 

Exercise 6. — Effect of Extent of Surface on Rate of Evaporation 

Fill a small drinking cup about half full of water, measuring 
exactly the amount used. Again measure the same amount of 
water, and place it in a large, shallow pan or basin. Set the cup 
beside the pan in a safe place where it will not be disturbed. The 
two vessels should have the same temperature and be exposed to the 
same air currents. Examine them daily and note the rate of evap- 
oration in each, till one is dry. Measure the amount of water re- 
maining in the other. 

Which is dry first? What conclusion do you draw regarding the 
effect of extent of surface on evaporation? 

Exercise 7. — Effect of Temperature on Rate of Evaporation 
Place one drinking cup containing a measured quantity of water 
on or near the stove or radiator. The water should not boil, but 
be kept warm. Place another cup of the same size and shape con- 
taining the same amount of water in a cooler place. Watch these 
two cups till one is dry. Draw a conclusion regarding the effect of 
temperature on the rate of evaporation. 

Exercise 8. — Effect of Air Currents on Rate of Evaporation 

Place two drinking cups of the same size and shape, each about 
one-half full of water (measuring amounts accurately), side by side 
in an open window or in some other position where the wind can 
sweep past them. Turn a large, 2-qt. cup or a small pail over one 
of the cups of water. Examine the cups of water daily and note 
which suffers the greater evaporation. What is your conclusion ? 

Exercise 9. — Rate of Evaporation Varies with Different Liquids 

Place two drinking cups of the same size and shape side by side 
in some safe place. Fill one about half full of water, and place in 



EVAPORATION, BOILING TEMPERATURE, ETC. 11 

the other the same amount of alcohol or gasoline. (Caution. — It is 
dangerous to leave gasoline in a closed room. It should be in the 
open air and no flames should be brought near it.) Note which 
evaporates more rapidly. Draw your conclusion. 

Exercise 10. — Effect of Evaporation on Temperature 

Let a few drops of alcohol or gasoline fall upon the back of your 
hand. Does it produce the sensation of heat or cold? Wrap a 
small piece of cotton cloth around the bulb of the thermometer and 
tie with a cord or thread. Take the reading of the temperature. 
Drop a few drops of alcohol or gasoline upon the cloth. Watch for 
a change in temperature. Repeat the experiment. Does the ther- 
mometer record the lowest temperature when the liquid is first 
dropped upon it or a little later? How do you account for this 
fact ? Wet your hand and hold it out of the window where the wind 
can strike it. What is the sensation? 

Draw a conclusion regarding the effect of evaporation upon 
temperature. 

Hunters usually wish to approach their game from the 
leeward side, that is, so that the wind will blow from the game 
toward the- hunter. Why do they wish to do so ? In order 
to tell the direction of the wind when it is too light to be 
observed readily by ordinal means the hunter often wets 
one finger at his mouth and then holds it high above his head 
where the wind can strike it. Try the experiment when you 
are out of doors and decide how it is that this tells the direc- 
tion of the wind. 

Why do we often feel chilly if we sit down with damp cloth- 
ing on? Why does fanning one's self produce the cooling 
effect that it does ? Is the cooling effect of fanning increased 
or decreased by the fact that one has been perspiring freely ? 

In regions having a dry, hot, windy climate like Arizona 
and New Mexico, it is found that butter can be kept hard and 
sweet for long periods simply by setting the dish containing 
the butter into a larger dish containing water and then spread- 
ing over the butter a piece of soft absorbent cloth, such as a 
clean towel, so that its corners and edges dip down into the 



12 THE PRODUCTION AND USE OF LIGHT 

water. The butter keeps sweet longer if placed where the 
wind strikes it. Explain. 

In the same regions drinking water is generally kept dur- 
ing the summer months in a large, porous, earthen vessel 
called an olla (o'-ya), which is hung out of doors, usually 
under a porch or tree. The olla being porous, its outer sur- 
face is constantly covered with a. film of water. Evaporation 
taking place over so large a surface cools the water within the 
vessel far below the temperature of the surrounding air. 

13. Laws of Evaporation. — From these and similar expe- 
riences we draw the following conclusions : 

I. The rate of evaporation from any given amount of liquid 
increases when the exposed surface is increased. 

II. Increasing the temperature of a liquid increases the rate 
of its evaporation. 

III. The rate of evaporation is increased by the continual 
removal of vapor above the surface of the liquid. 

IV. Some liquids evaporate much more rapidly than do 
others. 

V. Evaporation of a liquid always produces a cooling effect 
upon surrounding bodies. 

Temperature and the Thermometer 

14. Temperature. — We are all familiar with the common 
use of the term temperature. By it we mean the hotness or 
the coldness of a body. On a cold day we say that the tem- 
perature is low ; on a warm day we say it is high. We can 
generally tell when one body is warmer than another if we 
feel of the two bodies at the same time. We cannot, however, 
be certain of our judgment. Different substances feel to be 
of different temperature when they are in fact of the same 
temperature. The bare-footed boy knows this to be true. 
A piece of iron and a piece of wood lying side by side on a 
hot day will be of the same temperature. Will they feel so? 



EVAPORATION, BOILING TEMPERATURE, ETC. 13 

Which feels the warmer? What would be the case on a cold 
day? Which would then feel the colder? 

If at the close of a long ride on a very cold, windy day we 
were to step into an unheated room we would at once say that 
the room was warm. If we were to remove our wraps and sit 
down we should soon find, however, that the room was really 
cold. 

The truth is we cannot depend upon the appearance of 
objects, nor upon our sensations of heat and cold, to tell us 
the temperature of surrounding bodies. In all our work we 
shall be obliged to use an instrument especially constructed 
for this purpose, the thermometer. 

15. The Principle of the Thermometer. — 

Exercise 11. — How Heat Affects the Thermometer 

Fill a small flask with water. Fit a glass tube, 12 or 15 in. long, 
into a one-hole rubber stopper. Press the stopper down tightty into 
the flask. This should force the water well up into the tube. 

Light an alcohol lamp or Bunsen burner. Hold the flask for 
about one second in the flame. Notice carefully the first movement 
of the surface of the water. Does it rise or fall at first? What 
does it do later? Repeat the experiment till you feel certain that 
you see that the second motion is opposite to the first motion. 

The first motion is due to the fact that the heat first strikes 
the glass and expands it. This makes the flask larger — in- 
creases its volume. If the volume of the flask grows suddenly 
larger, what would you expect to see happening to the sur- 
face of the water? The second movement is due to the fact 
that, when heated, the water increases in volume much more 
rapidly than the glass vessel does. 

The common thermometer consists of a very small glass 
tube ending in a glass bulb at its lower end. This bulb and 
the tube are partly filled with mercury or alcohol. The air 
is nearly all removed from the upper portion of the tube. 
The tube is then closed by heating the glass till it softens and 



14 THE PRODUCTION AND USE OF LIGHT 

closes together. The principle of the thermometer may be 
summed up thus: When heated, the glass in the thermometer 
expands, increasing the capacity of the oulb and tube, but the 
heat soon penetrates to the liquid which then expands to a 
still greater extent. Alcohol expands more than 40 times as 
much as does the glass vessel, and mercury expands about 7 
times as much as does the glass vessel for a given change in 
temperature. 

1 6. The Fixed Points of Temperature in Nature. — The 
thermometer just described is still without any scale. In 
placing a scale upon it, the position of the surface of mercury 
or alcohol is marked when the thermometer is cooled or heated 
to some certain fixed temperatures in nature. The distance 
between the lower and higher temperature marks is then 
divided into a certain number of equal parts called de- 
grees. 

1. It has been long known that water always freezes and 
ice always melts at a certain temperature. For pure water 
this temperature is called the freezing point of water. 

2. It has also been known that at the average atmospheric 
pressure at sea level water always boils at a certain tem- 
perature. The temperature of the steam arising from water 
boiling under the atmospheric pressure which exists at the sea 
level, is therefore, called the boiling point of water. 

3. About two hundred years ago Fahrenheit found that a 
mixture consisting of 1 part common salt, or of sal ammoniac, 
a substance closely resembling salt, and of 2^2 parts snow or 
crushed ice always melted at a certain temperature consid- 
erably below the temperature of freezing water. Fahrenheit 
called this third temperature the melting point of a mix- 
ture OF SALT AND ICE. 

There are a great many other fixed points of temperature 
in nature. For example, pure iron always melts at exactly 
the same temperature; so does lead, and so does zinc. Both 
pure mercury and pure alcohol have certain temperatures at 
which they boil and others at which they freeze. When in 



EVAPORATION, BOILING TEMPERATURE, ETC. 



15 



good health the human blood always has the same tempera- 
ture. But in marking the common thermometer the three 
temperatures first mentioned, namely, the freezing point of 
water, the boiling point of water, and the melting point of a 
mixture of ice and salt, are the only temperatures which we 
commonly use. 

17. Fahrenheit's Thermometer. — In making the ther- 
mometer which bears his name Fahrenheit marked the posi- 
tion of the mercury "0°" when the thermometer was cooled 
down to the temperature of the mixture 
of ice and salt. It is believed that he was 
induced to call this temperature 0° 
partly because it was the unusually low 
temperature reached by the weather in 
Holland in the winter of 1709. He called 
the temperature of freezing water "32°" 
and the temperature of boiling water 

'212°. " 

18. Centigrade Thermometer. — Much 
Later Celsius made his so-cal]ed centi- f ig. 8.— Freezing point 
brade thermometer. On this thermom- 
eter the freezing point of water is marked as "0°" and the 
boiling point of water as "100°." 

Often both scales are placed upon the same thermometer 
stem. It is also true that the scale may extend far above the 
boiling point of water and far below the melting point of 
the mixture of ice and salt. 

19. Determining the Freezing Point on a Thermometer. — 




Exercise 12. — Testing a Thermometer for the Freezing Point 

Suspend a funnel in the ring of an iron support. Clamp a ther- 
mometer by means of the burette clamp at such a height that the 
bulb hangs well down in the throat of the funnel. Pack the fun- 
nel full of finely broken ice or snow, heaping it well up around 
the stem of the thermometer. The stem should be surrounded with 
ice or snow up as nearly as possible to the point marked 0°C, or 
32 °F. Keep plenty of ice or snow in the funnel and see that it 



16 



THE PRODUCTION AND USE OF LIGHT 



remains tightly packed around the thermometer for some minutes. 
Does your thermometer record correctly the freezing point of 
water? If not, what is the amount of the error? (Fig. 8.) 

Even very good thermometers are often slightly incorrect. 

Boiling Point 
20. The Temperature of Boiling Water. — 

Definitions. — A liquid is said to evaporate when it 
changes from the liquid form to the vapor form at the sur- 
face only. 

A liquid is said to boil when it changes to the vapor form 
beneath the surface and the bubbles of vapor rise to and\ 
escape from the surface. 

A liquid is said to be vaporized whenever it changes to 
vapor. A liquid is vaporized when it evaporates or boils. 

Exercise 13. — To Determine the Temperature of Boiling Water 

Fill a 4-oz. distilling flask half full of water. Slip a chemical 
thermometer into the hole in a rubber 
stopper. Push the thermometer far 
enough through the stopper so that the 
bulb will dip into the water when the 
stopper is fitted into the mouth of the 
flask. Before inserting the stopper and 
thermometer it is well to place a few 
small nails or some common glass beads 
in the flask. The presence of some- 
thing of this kind in the flask will cause 
water to boil more steadily and prevent 
"bumping." (Fig. 9.) 

Clamp the iron ring to the stand at a 
point about 2 in. above the flame. Place 
a wire gauze upon the ring and set the 
flask on the gauze. Steady its top by 
clamping it loosely with the burette 
clamp. Adjust the flame so that it will 
not be too high. Slip it under the 
flask and watch for results. 

The first small bubbles which you see rising through the water 



Bt/A£rrj: 




Fig. 9. 



-Boiling point of 
water. 



EVAPORATION, BOILING TEMPERATURE, ETC. 17 

are bubbles of air, not of steam. Keep watch of the reading of 
the thermometer. Do you see any evidence of steam, or water 
vapor, before the water actually boils? Does the steam rise from 
a pan of hot water on the stove before the water really begins to 
boil? At what temperature by your thermometer does the water 
finally boil? Continue to heat the water to see if it is possible to 
raise the temperature higher. Can you see steam in the upper 
portion of the flask? Can you see it immediately after it escapes 
from the side tube? (Caution. — Do not permit the flame to reach 
higher than the surface of the water in the flash, else the flash 
will probably crack.) 

If you are not careful you may be led to give incorrect 
answers to the last two questions. Steam, or water vapor, is 
invisible. But something escaped from the side tube. What 
do you now think that it was ? What happens to steam when 
it is again cooled after escaping from the flask? We some- 
times say that we see steam escaping from an engine or loco- 
motive. This is not strictly true. We see only the small 
particles of water which have been formed again from the 
steam and which are floating in the air. 

Unless you are living at or very near the sea level you have 
probably found that the temperature of the boiling water 
according to your thermometer is somewhat below 212°F. f 
or 100°C. 

21. The Temperature of the Steam Arising from Boiling 
Water. — In the last experiment the bulb of the thermometer 
was in the water, therefore the thermometer recorded the 
temperature of the water itself. Would it record a different 
temperature if it were raised above the surface of the water, 
high enough so that no water could touch it, but still be sur- 
rounded by steam ? 

Exercise 14. — Temperature of Steam Arising from Boiling Water 

Raise the thermometer higher in the rubber stopper used in Ex. 
13. The bulb of the thermometer should be up in the neck of the 
distilling flask but below the side tube. Replace the lamp and bring 
the water to a boil. What temperature does the thermometer record 



18 



THE PRODUCTION AND USE OF LIGHT 



now? See if the temperature can be raised by causing the water to 
boil more rapidly. (Caution. — Do not permit the flame to reach 
higher than the surface of water in the flask.) 



The temperature of the steam which escapes from boiling 
water is always a little lower than the temperature of the 



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iFic 10. — Thermometer scales and some fixed temperatures in nature. 

boiling «water itself. This is exactly what we should expect, 
for the heat is being applied to the glass vessel and then 
transferred to the water. The water is constantly in contact 
with glass which is slightly above the temperature of boiling 
water. Moreover, if there are impurities in the water their 
presence will tend to change the boiling temperature ; gener- 



EVAPORATION, BOILING TEMPERATURE, ETC. 19 

ally they raise the temperature, although certain dissolved 
gases lower it. 

Definition. — The temperature marked 100° C, or 212° F., 
and called "boiling point" is the temperature of steam aris- 
ing from boiling water when the pressure is equal to that of 
the atmosphere at the sea level. 

In the experiment did your thermometer indicate a tem- 
perature of 100°F., or 212°F.? Can you explain why it did 
not? 

22. Comparison of the Fahrenheit and Centigrade Scales. 
— The Fahrenheit scale is nearly always used on thermometers 
sold in the United States for common use ; the centigrade scale 
is nearly always used on thermometers intended for use in lab- 
oratories. In encyclopedias, government reports and many 
other publications to which we frequently refer, we are very 
likely to find temperatures given in either of the two scales. 
We ought to learn to think temperatures in either scale 
(Fig. 10). 

Exercise 15. — Comparing Temperature on the Fahrenheit and 
Centigrade Scales 

By studying Fig. 10, tell as near as you can what the temperature 
of the blood is on the centigrade scale. What should be the tem- 
perature of the school room on the centigrade scale? Which are 
the greater, the Fahrenheit or the centigrade degrees? How many 
degrees are there on the Fahrenheit scale between the freezing point 
of water and the "boiling point" of water? How many degrees 
are there on the centigrade scale between the freezing point and 
the "boiling point"? How many Fahrenheit degrees equal 1 centi- 
grade degree? Which is the colder, 0°C. or 0°F.? Are there any 
temperatures which are above 0°F. but below 0°C? You should 
use a thermometer having both scales on it frequently and always 
record the readings on both scales. In this way you will soon be able 
to think temperature by both scales. 

23. The Boiling Point of Alcohol. — In Ex. 14 we found 
that the temperature of the steam, or vapor, arising from boil- 



20 



THE PRODUCTION AND USE OF LIGHT 



ing water remained the same whether the water boiled slowly 
or rapidly. We should like to find out whether the same 
thing is true of alcohol. 



Exercise 16. — To Determine the Boiling Point of Wood or Grain 

Alcohol 

Fill a distilling flask half full of alcohol. Put in some glass beads 
or nails. Insert the stopper and thermometer, adjusting the ther- 
mometer in height so that the 
bulb will extend somewhat be- 
low the side tube and still be 
above the base of the neck of 
the flask. Clamp the flask in 
the ring stand at the proper 
height above the alcohol lamp 
or burner. Set the stand in a 
metal tray such as a large 
dripping pan. Since alcohol 
is inflammable it should be 
handled with care. Before 
lighting the lamp, place a piece 
of cardboard between the flask 
and the delivery tube to avoid 
any possibility of the escaping 
alcohol vapor being accidentally 
set on pre by the /fame (Fig. 11). 
Light the lamp or burner and notice all that takes place as the 
alcohol is brought slowly to a boil. Record the temperature of the 
alcohol vapor when the vapor first begins to escape from the side 
tube. Do you suppose that this vapor will burn? 

Taking care that no one is in front of the delivery tube, light 
the escaping vapor with a match. Does the vapor continue to 
burn as long as the boiling continues 1 ? 

After three or four minutes read the thermometer again. Has 
the "boiling point" changed? Does rapid boiling change the "boil- 
ing point" of alcohol? 

Should the "boiling point" of your sample of alcohol not 
remain constant but rise with continued boiling your alcohol 
probably contains water. The simplest test for pure alcohol is 
the test of the boiling point. Wood alcohol, as pure as can 




Fig. 11. — Distillation of alcohol. 



EVAPORATION, BOILING TEMPERATURE, ETC. 21 

be obtained by distillation, has a constant boiling point of 
66°C, or 150%°F. Ordinary grain alcohol has a constant 
boiling point of 78°€., or 172 2 / 5 °F. These are the boiling 
points at the sea level. In our school rooms these tempera- 
tures will be slightly lower. Then, too, our thermometers may 
not be exactly correct. But in any case the boiling point of 
pure alcohol will not change with continued boiling. All pure 
substa)ices in the liquid state have certain constant boiling 
points. Some are much higher than that of water, for ex- 
ample, the boiling point of mercury is 357° C. ; some are much 
lower, as oxygen, — 182°C, or hydrogen, — 252°C. 

Distillation 
24. Boiling Point of a Mixture of Alcohol and Water. — 
If pure wood alcohol boils at 66 °C. and continues to boil at 
that temperature till all of the alcohol has been turned into 
vapor the question arises: What would take place if we had 
a mixture of alcohol and water? With our distilling flask, 
thermometer, and lamp or burner we can soon answer the 
question. 

Exercise 17. — Distillation of Alcohol 

Pill the distilling flask about one-fourth full of alcohol and add an 
equal amount of water. Place some beads or small nails in the flask, 
insert the stopper and thermometer, and place the cardboard be- 
tween the flask and the side tube. Light the lamp or burner and 
notice carefully the temperature at which boiling first takes place. 
Watch the temperature carefully as the boiling continues. 

Light the escaping vapor as you did in Ex. 16. Allow the vapor 
to continue burning as long as it will do so. Does the flame finally 
go out? Can you relight it? Can you explain why the vapor 
does not continue to burn well? After a few minutes, you will 
probably find that the vapor will not burn at all. Why? About 
what part of the mixture of water and alcohol has boiled away 
when the vapor no longer burns? 

Continue to watch the temperature at which the liquid in the 
flask boils. Does the temperature finally reach that of boiling 
water? How do you account for this fact? About what portion 



22 THE PRODUCTION AND USE OF LIGHT 

of the mixture of water and alcohol has boiled over when the tem- 
perature reaches this point? 

Did drops of liquid form at the end of the side tube? What do 
you suppose they were, water or alcohol? 

Explanation of Ex. 17. — We have seen that alcohol boils at 
a much lower temperature than does water. It is also true 
that alcohol vapor condenses, i. e. changes from vapor form to 
liquid form, at a much lower temperature than does water 
vapor. It is probable that in your experiment, the side 
tube was so heated that most of the alcohol escaped as vapor 
while some of the water vapor condensed and formed drops 
of water at the end of the tube. If we had kept the side 
tube cool enough, we could have caused both the water vapor 
and the alcohol vapor to have condensed. 

Definition. — This process of changing a liquid into vapor 
by means of heat and then of changing the vapor back into a 
liquid by cooling it is called distillation. 

The liquid obtained from distillation is called a distillate. 

Because different liquids have different boiling points we 
are often able to separate the liquids in a mixture as we have 
just separated the alcohol from the water. It is not true, 
however, that the alcohol has been entirely separated from 
the water by this one distillation. The first portion of alcohol 
which passed over as vapor and which we burned contained 
some water ; the water which remained in the flask at the close 
of the experiment likewise contained some alcohol. To get 
the alcohol nearly free from water it is necessary to re-distil 
several times. The factories where alcohol is made in large 
quantities are called distilleries because the alcohol when first 
made is mixed with water and must be separated from it by 
means of distillation (see Art. 299, page 272). We shall 
soon see that all the kerosene and gasoline which we use have 
been separated from petroleum by this same process of distil- 
lation. 



PETROLEUM AND ITS PRODUCTS 23 



IV. PETROLEUM AND ITS PRODUCTS 

25. Petroleum. — When petroleum first comes from the well 
it is usually of a dirty, dark, bluish-brown color; usually it 
gives off a strong odor which is disagreeable to most people. 
In the region of oil wells the whole atmosphere is charged 
with this odor for miles around. This simply means that as 
the petroleum comes from the well some of it immediately 
evaporates, or passes off into the air in the form of vapor, 

Or gas, NATURAL GAS. 

We are not greatly surprised to find that this is so, for 
we have seen that water left uncovered is constantly evapo- 
rating. We have also seen that alcohol left uncovered evapo- 
rates even more rapidly. It is the same with all other 
liquids, though some evaporate very rapidly and others very 
slowly. 

We have also seen that heating water or alcohol, or a mix- 
ture of the two, increases the rate of evaporation. If we 
heat either liquid hot enough, it boils and vaporizes with 
great rapidity. 

26. The Distillation of Petroleum. — Remove the stopper 
from the bottle of petroleum. Notice carefully the color and 
odor. If we were to place a little in a vessel and heat it, we 
should see that it boils quickly. Hence, petroleum would 
seem to behave very much as water or alcohol does so far as 
evaporation and boiling are concerned. To understand the 
real nature of petroleum, however, it will be necessary to 
keep constantly in mind all the facts we observed when we 
distilled the mixture of alcohol and water. What did we 
notice in regard to the boiling point of the mixture? Did it 
remain constant? At what temperature did it begin to boil? 
What was its boiling point when we stopped the experiment? 
What was our conclusion? We must keep these things in 
mind while we perform the following experiment: 



24 THE PRODUCTION AND USE OF LIGHT 



Exercise 18. — To Distil Petroleum 

Fill a 4-oz. distilling flask half full of petroleum, 1 using a funnel 
so that no petroleum enters the delivery tube. Put some small 
nails or beads into the flask. Clamp the flask to the stand as in 
Ex. 16 and insert the stopper and the thermometer, which, at the 
beginning of the experiment, may have a scale which reads to about 
100°C. or 212°F. The lower end of the bulb of the thermometer 
should reach about V 2 in. below the side tube. 

As the experiment proceeds the thermometer may have to be 
raised or lowered in the stopper in order that its reading may be 
taken. Place the piece of cardboard between the distilling flask 
and the vessel into which the distillate will drip. Guard against 
possible accident, such as the cracking of the flask. While it is ex- 
tremely improbable that the flask will crack, it is well to set the 
entire apparatus in an ordinary dripping pan or some flat-bottomed 
vessel and to keep a wet towel near with which to smother the 
flames in case of accident (See Fig. 11). 

Place the lamp under the flask and gently heat the petroleum. 
Notice that it begins to boil very soon. As soon as you see the 
vapor pass over into the delivery tube and there condense, read 
the thermometer. Catch the distillate in a small, clean bottle. 
Notice the color and appearance of the distillate. Watch the ther- 
mometer carefully. Is the temperature rising steadily? When it 
reaches 70° C, or 158°F., remove the bottle in which you have been 
catching the distillate and place another in position. Label the 
first bottle "Distillate No. 1." Does the temperature still continue 
to rise? When it reaches 80° C, or 176°F., again remove the bottle 
in which you have been catching the distillate and label it "Dis- 
tillate No. 2." 

Caution. At this point remove the 100°C. thermometer and 
insert one reading to 360° 'C. or 680° F. 

In the next bottle catch the distillate till the temperature has risen 
to 120°C., or 248°F. Label this "Distillate No. 3." Catch in a 
fourth bottle the distillate which passes over between 120° C. and 
150° C. and label it "Distillate No. 4." Finally in a fifth bottle 
catch the distillate which passes over between 150°C. and 300°C. 
It will be found necessary to heat more strongly now and possibly 

i Crude petroleum, just as it comes from the well, should be used. 
Road oil will not answer as the lighter distillates are usually removed 
from oil sold for the purpose of oiling roads. 



PETROLEUM AND ITS PRODUCTS 25 

to enclose the flask partly in a shield of tin or asbestos paper in 
order to raise the temperature to 300 °C. This last portion of the 
distillate will probably contain about one-half of the entire dis- 
tillate. Remove the lamp and pour as much of the residue as 
possible out of the flask while it is still hot. When it cools it will be 
solid and cannot be removed readily from the flask. Wash the 
flask out clean with gasoline so that it will be ready for future use. 
Caution. — Gasoline should be used for this purpose out of doors, 
or, if in the house, the doors and windows should be left open so 
that the wind may quickly remove the vapor from the room. Never 
use gasoline when there is a flame near. 

27. The Products of Petroleum. — In this last experiment 
we have separated the crude petroleum into six different por- 
tions. The process is fractional distillation, and the 
products are practically the products of petroleum as they are 
sold on the market. We shall be able to remember these 
products better if we put them in a table thus : 

Table I. — Products of Petroleum 1 

Boiling points 

1. Distillate No. 1— "Petroleum Ether," 40°- 70°C. or 104°-158°F. 

2. Distillate No. 2— "Light Gasoline," 70°- 80°C. or 158°-176 6 F. 

3. Distillate No. 3— "Heavy Gasoline," 80°-120°C. or 176°-248°F. 

4. Distillate No. 4— "Naphtha" 120°-150°C. or 248°-302°F. 

5. Distillate No. 5 — "Illuminating Oil" or "Kerosene" 

150°-300°C. or 302°-576°F. 

6. The Residue — The thick, tarry substance remaining in the flask. 

28. Purifying the Petroleum Products. — These products of 
petroleum obtained by distillation will have a strong odor, 
and the kerosene will probably show considerable color. 
Formerly all illuminating oil was highly colored and had this 
same strong odor. Nowadays all of the products of petro- 
leum are carefully cleansed and purified before they are put 

1 Every refiner of petroleum has his own method of separating 
petroleum into its commercial products The method varies with the 
quality of petroleum used and the demands of the market. The method 
here given, however, is typical. 



26 



THE PRODUCTION AND USE OF LIGHT 



on the market. The purifying removes nearly all of the 
color and most of the offensive odor. The process of purify- 
ing kerosene is much too difficult for us to undertake. 

29. The Uses of These Petroleum Products. — 

Petroleum Ether is subdivided into several portions to 
each of which a special name is given. It is used chiefly in 
surgery and in dissolving substances like resin and heavy oils. 

Light Gasoline is chiefly used in gasoline gas machines 
(see Art. 39). 

Heavy Gasoline is the common gasoline sold at the grocery 
store and gasoline service station. It is used in gasoline 




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Z.Sf. 33 f. 



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Fig. 12. — The products of petroleum. 



stoves, in gasoline lamps, in automobiles and gasoline engines. 
It is also sometimes used in paints. 

Naphtha, often called "heavy naphtha," is used as a 
substitute for turpentine in making paints and varnishes, 
and also for cleaning heavy oils from machinery. 

On account of their evaporating so rapidly when exposed 
to the air or, as we say, being so very volatile, these first four 
products of petroleum are called the light oils or spirits. 

Kerosene or Illuminating Oil is chiefly used to furnish 
light when burned in the ordinary kerosene lamp. It is also 
frequently burned in stoves of special construction for heat- 
ing purposes. 

The Residue is manufactured into lubricating oil, 



PROPERTIES OF GASOLINE— SOURCES OF DANGER 27 

paraffin oil, and solid paraffin. A small amount of COKE 
still remains after these are removed. 

Suggestion. — It would be well for you to catch the different dis- 
tillates which you obtained in Ex. 18 in small bottles, cork them air 
tight, label each with its correct name and boiling points, then set 
them away for future reference. Your parents and friends will 
be glad to see samples of the crude petroleum and these products 
(Fig. 12). 

V. PROPERTIES OF GASOLINE— SOURCES OF DANGER 
Density, Flashing Point and Burning Point 

30. The Grades of Gasoline as the Merchant Knows 
Them. — We have seen that gasoline is a name applied to 
some of the lighter, more volatile products of petro- 
leum. We have also seen that it is separated both 
from the lighter petroleum ether and the heavier 
naphtha and kerosene by means of fractional dis- 
tillation. We have further seen that there are two 
grades, at least, of gasoline — light gasoline and 
heavy gasoline. When we buy gasoline at the gaso- 
line service stations we get heavy gasoline. This 
heavy gasoline may be either low test or high test 
gasoline. The low test gasoline is a heavier liquid 
than the high test. The refiner and the merchant 
need to know quite accurately how heavy the gasoline 
is in order to know its value and how suitable it is for 
a certain use. The density of gasoline is determined 
by means of a Baume hydrometer. 

31. Baume's Hydrometer. — This instrument 
(Fig. 13) consists of a glass tube 8 to 10 in. in length. 
Near its lower end this tube has been blown into a fig. 13. 
large bulb, and still farther down, at its very end, it Baume 
has been blown into a small bulb and sealed. Some meter, 
mercury or small shot is dropped down the tube 

into the lower, small bulb. Some melted sealing wax is 
then dropped down inside the tube and made to close the 



28 THE PRODUCTION AND USE OF LIGHT 

opening between the two bulbs. Care is taken to have the in- 
strument so weighted that it floats with the stem above the 
large bulb above the surface when placed in water. The in- 
strument is then graduated by floating it in lighter liquids 
and marking the scale on a strip of paper which is slipped 
down inside the stem. The stem is then sealed and the in- 
strument is complete. 

The instrument is called a Baume hydrometer (hydro — 
water, and metron — measure), because Baume invented the 
scale used upon it. Oils of all kinds including the products 
of petroleum, also syrups, vinegars, and many other liquids 
are regularly bought and sold on the market at prices which 
vary according to the density of the liquids as determined by 
this hydrometer. It must be remembered that the light gaso- 
line has a lower boiling point and is a lighter liquid per gallon 
than the heavy gasoline. But it must also be remembered that 
the grading of the lighter gasoline by the Baume hydro- 
meter is about 85° to 88°, while the heavy gasoline grades 
from about 56°B. to 65°B. At the present time low test 
gasoline generally tests from 56° to 60°. That is, it is al- 
ways true that the lighter the oil, the higher it will grade in 
Baume degrees; the heavier the oil, the lower it will grade 
in Baume degrees. Kerosene grades about 45° Baume, and 
is written "45°B." 

32. The Inspection of Oil. — If the different grades of gaso- 
line, naphtha, and kerosene have been properly distilled and 
purified we are able to tell fairly closely the range of boiling 
points of the different oils, simply by testing their density, by 
means of this hydrometer. The different states have passed 
laws governing the manufacture and sale of the products of 
petroleum. These laws have been passed for the protection 
of the purchaser and user. There are oil inspectors in nearly 
all cities and in many of the smaller towns whose duty it is 
to inspect the products of petroleum offered for sale and to 
set that they are really what they are said to be. In most, if 



PROPERTIES OF GASOLINE— SOURCES OF DANGER 



29 



not all, of the states the products of petroleum must be thus 
inspected before they are offered for sale. This test for den- 
sity by means of the Baume hydrometer is one of the tests. 

33. Flashing Point. — The most important test, however, 
which can be given the products of petroleum is to test their 
flashing point (Art. 5, Ex. 2). This consists in deter- 
mining the temperature of the oil at which the vapor arising 
from it will flash when a flame is brought near it. It is this 
test which determines whether an oil is safe or unsafe to 
have about a building or to be put to certain uses. A good, 
legal quality of kerosene is not to be considered dangerous to 
have in a room. Any quality of gasoline, on the other 
hand, is always to be considered dangerous, and must be cared 
for accordingly. A very simple experiment will show us that 
this .is so, and will help us to understand why it is so. 



Exercise 19. — Flashing Point of Gasoline and Kerosene 

Put four or five tablespoonfuls of kerosene in a tin eup. Place 
the bulb of the thermometer in the oil and take its temperature. 
Record this. Light a match and try to set 
the kerosene on fire. Are you successful 1 ? 
Try again. Make a sufficient number of trials 
to satisfy yourself whether or not you are 
able to set the kerosene on fire. It is not 
probable that you will succeed, but if you 
should finally get it to burn, smother the 
flames quickly by placing a piece of glass 
over the dish so as to exclude all air. Take 
the temperature of the oil again and record 
all that happened. 

Now place two tablespoonfuls of gaso- 
line in another cup. Take its tempera- 
ture. Remove the thermometer. Try lighting the gasoline as 
you did the kerosene. Be sure that the glass is close by so 
that you can cover the dish quickly in case the oil catches on fire. 
Also be sure that the can of gasoline has been removed from the 
room, or tightly corked. When the flame has been extinguished, 
remove the glass from the dish, light another match and bring it 
slowly down above the dish to see at what height above the surface 




Fig. 14. — Flashing 
point of kerosene. 



30 THE PRODUCTION AND USE OF LIGHT 

of the gasoline the flash does take place. Try again. Is it the 
liquid gasoline which burns? 

Set the gasoline to one side, and make a further, study of the kero- 
sene. If you have a good quality of oil, you have probably not yet 
succeeded in making it burn. Fit the wire gauze on the ring of 
the stand. Set the cup of kerosene on the gauze and heat very 
gently (Fig. 14). Test the oil frequently with the lighted match 
to see if the vapor arising from it will catch on fire. When it is 
hot enough it will suddenly flash when the lighted match is applied. 
Smother the flame, using the glass as before. Take its tempera- 
ture. This temperature is somewhat, perhaps slightly, above the 
flashing point. If the flame continues to burn above the surface 
of the oil, you have heated it several degrees above the flashing 
point. It is, indeed, above the burning point. Let the oil cool. 
But to do so you must put out the flame. Take the temperature 
each minute or two, as it cools, and after each reading of the 
thermometer test the oil with a lighted match to see if it still 
burns. When it no longer burns, you have passed the burning 
point. It may still flash, however, but the flame immediately goes 
out. It is still above the flashing point if this is the case. When 
the oil no longer flashes it has cooled below the flashing point. 

Definitions. — The flashing point of an oil is the lowest 
temperature of that oil at which it will give off enough vapor 
so that when mixed with the air above, it produces a momen- 
tary flash when a flame is brought near the surface of the oil. 

The burning point, or fire test, of an oil is the lowest tem- 
perature of that oil at which it will give off enough vapor to 
maintain a continuous flame when once ignited. 

The burning point of kerosene may be from 20° to 60 °F. 
higher than its flashing point. In ordinary kerosene it is 
usually from 40° to 50°F. higher. Most of the states have 
laws which forbid the sale of oil as illuminating oil, or kero- 
sene, which has a flashing point lower than about 110°F. or 
a burning point lower than about 150°F. This is the most 
important of all of the tests which the inspector applies to 
kerosene. 

The better qualities of kerosene have a flashing point of 
120°F. to 140°F. If a lighted match be dropped into it, the 



PROPERTIES OF GASOLINE— SOURCES OF DANGER 31 

flame is extinguished. It has no unpleasant odor and burns 
up completely without charring the wick of the lamp. Such 
an oil is obtained by rejecting the first of the distillate after 
the boiling point of the petroleum has reached 150° C. and 
also the last portion just before the boiling point reaches 
300 °C. This choice distillate is then carefully purified. 

A fair quality of oil is obtained by using all of the distillate 
from 150°C. to 300°C. and carefully purifying it. The 
cheaper grades of oil contain larger amounts of the portions 
rejected from the higher grades. They therefore have low 
flashing and burning points, and char the wicks. 

34. Use of Kerosene in Kindling a Fire. — If instead of 
catching on fire itself a good quality of kerosene will put out 
a burning match, how is it that kerosene may be used as a 
kindling in starting a fire? It is a common thing for people 
to dash a little kerosene upon the fuel in a stove when start- 
ing a fire. Can you readily start a coal fire by the use of 
kerosene alone as kindling? Why does kerosene ignite so 
much more readily when poured upon wood or paper than 
when poured upon coal? Is it ever safe to use kerosene as 
kindling when starting a fire? These and other questions 
which may arise are easily answered by remembering that 
kerosene vapor burns only when the kerosene is heated to its 
burning point. 

When the oil is poured upon wood, especially if the wood is 
splintered or in the form of shavings, it becomes an easy 
matter to heat small portions of the oil which saturate the 
smaller splinters or shavings to the burning point. When the 
oil lies spread as a thin coat over the chunks of coal it is dif- 
ficult to raise any portion of the oil to its burning point, un- 
less the coal is very finely divided, because the heat applied to 
the oil passes on into the coal and it becomes necessary to 
raise the temperature of the whole chunk of coal to the burn- 
ing point of kerosene. The match does not furnish a suf- 
ficient amount of heat to do this. 

Danger of an explosion from the use of kerosene arises only 



32 THE PRODUCTION AND USE OF LIGHT 

when the oil is heated above its flashing or burning point. 
Evidently if the oil is poured upon unheated fuel and is then 
ignited, the flame will consume the vaporized oil as rapidly as 
it is vaporized. If, however, the oil is poured upon heated 
fuel or live coals, or even upon fuel in a heated stove, there 
is then danger that the oil will be vaporized in large quanti- 
ties and mixing with the air will produce an explosive mix- 
ture. If the flame be then applied a violent explosion is 
certain to occur. Therefore, kerosene should never be used as 
kindling if there are live coals in the stove or if the stove 
is itself still hot. 

Danger in Using Cheap Kerosene and Gasoline 

35. Danger in Using Cheap Kerosene. — Many experiments 
with lamps of different shapes and materials show clearly the 
danger which comes with the use of inferior qualities of kero- 
sene. With the temperature of the room 73° or 74°F. the 
temperature of the oil in the lamp bowl has been found to 
vary from 76° to 100°F. With the temperature of the room 
82° to 84°F. the temperature of the oil is from 84° to 120°F. 
With the temperature of the room 90° to 92°F. the tempera- 
ture of the oil in the lamps in some cases ran as high as 
129 °F., though these were exceptional. 

From these facts it is evident that the oil within the lamp is 
likely to be heated to a temperature considerably above the 
temperature of the room. It is also evident that no oil should 
be used which does not have a flashing point considerably 
above the highest temperature ever reached by the air of the 
room. Explosions occur because the oil has been heated to a 
temperature above the flashing point. 

36. Oil May be Dangerous when Standing in the Can. — 
The following facts must be kept constantly in mind by all 
users of petroleum products : 

1. Any oil is a dangerous oil and must be kept away from 
all fires or open flames if it has a flashing point which is at or 



PROPERTIES OF GASOLINE— SOURCES OF DANGER 3S 

below the highest temperature ever attained by the room or 
building in which it is stored. 

2. In fact, merely removing the can of oil from the room 
does not remove all of the danger. If the room has been 
closed for some time, the vapor which has escaped may have 
saturated the air in the closets, cupboards, or even trunks, and 
this saturated air will explode when ignited. 

3. Gasoline has a flashing point far below the temperature 
of any living room. If the can is not air tight, the vapor of 
the gasoline is certain to escape into the room. Unless the 
room is very well ventilated, the air in it may become so satu- 
rated with the vapor of the gasoline that it will burn, with an 
explosion when ignited. In its low flashing point lies the* 
danger of using gasoline. 

4. The flashing point of legal kerosene is sufficiently above 
the ordinary room temperatures so that no corresponding 
danger exists in its use. 

37. May Gasoline be Used with Comparative Safety? — 
Yes, by observing the following precautions: 

1. Keep the main can of gasoline in some well-ventilated 
out-building. 

2. // the can must be kept in the living rooms, see that it is 
corked as tight as possible, that it is in as cool a place as 
possible, and that the room is well ventilated. 

3. Never take a flame of any kind near the can, nor near 
any large quantity of gasoline. 

4. Never attempt to fill a gasoline stove or lamp by lamp 
light. 

5. In case gasoline is spilled by accident, or has leaked from 
the receptacle, open wide the doors and windows of the room 
to change the air completely before bringing a flame into the 
room. Also thoroughly ventilate all cupboards and closets in 
which there is a possible chance of the air having become sat- 
urated with the gasoline vapor. 

If these precautions are observed there will be but little 
danger in handling gasoline. 



34 



THE PRODUCTION AND USE OF LIGHT 



VI. THE GASOLINE GAS MACHINE 

38. Gasoline Easily Vaporizes. — We have seen that gaso- 
line exposed to the air vaporizes rapidly. We have also seen 
that if any considerable quantity of gasoline remains exposed 
to the air of a room for a short time that the air becomes so 
charged with vapor of gasoline that it burns readily. In 
fact, the mixture frequently explodes violently when a flame 
is brought near. This is the cause of most accidents which 
occur from the careless use of gasoline. 

Because gasoline does evaporate so readily when exposed 




Blower Mixer 

Fig. 15. — A gasoline gas machine. 



Carbureter 



to air it is possible, by using a properly constructed machine, 
to produce gasoline gas. Several gasoline gas machines are 
now in use furnishing gasoline gas for use in country resi- 
dences and in school buildings which are out of reach of a 
city supply of common illuminating gas. 

39. Gasoline Gas Machines. — There are several different 
types of gasoline gas machines. Every machine must, how- 
ever, consist of two distinct and different parts and usually 
possesses a third. The essential parts are a blower or pump, 
and a carbureter. The third part is called a mixer. 

The Blower is a simple device for forcing a current of air 



THE GASOLINE GAS MACHINE 



35 



out through the carbureter and back into the pipes of the 
building. It maintains the pressure on the gas. Fig. 15 
shows a common form of blower. It consists of a large fan 
operated by means of a heavy weight. The weight is wound 
up at intervals as required. It exerts a constant pressure 
upon the pump. As long as lights are burning, the pressure 
is being reduced and the pump works to maintain the pressure. 
The Carbureter is a large tank capable of holding several 
barrels of gasoline. It is buried in the ground usually some 
distance from the wall of the basement of the building. 
There are different styles 
of carbureters. The cuts 
(Figs. 15 and 16) show one 
form made of heavy sheet 
steel. It is shaped much 
like a cheese tub, but is 
divided into four cells by 
the three false bottoms. 
Upon each of these shelves, 
or bottoms, stands a spiral 
coil of absorbent material 
like lamp wicking. This 
absorbent material is in- 
tended to form a coil-like 
partition extending from 
top to bottom of each cell so 
that the air must, in passing through one cell, pass through 
the long coil-like passage. The bottom of the passage is gaso- 
line; each side is the absorbent material saturated with 
gasoline. The cells are so connected that air in passing 
through the carbureter must pass through all four of these 
long, coil-like passages. If straightened out the passage would 
be 2 in. high, 3 in. wide and 300 ft. long. The purpose of 
the carbureter is to expose the gasoline to the air as much as 
possible so that the air will become fully saturated with the 
gasoline vapor producing gasoline gas. 




Fig. 16. 



-Sectional view of the 
carbureter. 



36 THE PRODUCTION AND USE OF LIGHT 

The Mixer is a device for maintaining the proper mixture 
of gasoline vapor and air. Gasoline consists of many dif- 
ferent compounds (See Art. 71). Each compound has a 
certain rate of evaporation, at a given temperature. The 
lighter portions of the gasoline evaporate more quickly than 
the heavier portions. This means that for some time after 
each refilling of the carbureter the air is more completely 
charged with vapor than is the case later when the lighter 
portions of the gasoline have evaporated and only the heavier 
portions remain in the carbureter. The purpose of the mixer 
is to keep the gasoline gas, i. e., the mixture of air and gaso- 
line vapor, the same at all times. 

The gasoline gas machine is used successfully, not only to 
furnish gas for lighting purposes, but also for cooking in a 
gas range exactly as city illuminating gas is used. Only 86° 
to 8S°B. gasoline can be used successfully in these machines. 

VII. MANUFACTURED GASOLINE AND MOTOR SPIRIT 

40. Importance of Gasoline. — Up to about the year 1900 
kerosene, or illuminating oil, was by far the most important 
product of petroleum. Only a certain percentage of the crude 
oil — generally from 30 to 50 per cent. — could be refined as 
illuminating oil and about 20 per cent., as gasoline. There 
was a good market for the kerosene but only a light demand 
for the gasoline. As a consequence, kerosene sold for a higher 
price than did gasoline. With the general introduction of 
electric lighting in towns and cities the demand for kerosene 
fell off; while at the same time, with the perfecting of the 
automobile and the coming of the gasoline engine into general 
use, the demand for gasoline increased greatly. About 1910 
the demand for gasoline became greater than the supply, and 
the price became higher than that of kerosene. This in- 
creased demand for gasoline has led oil refiners to adopt the 
plan of putting nearly all of the distillates of petroleum up 
to illuminating oil together and selling them as gasoline. 



MANUFACTURED GASOLINE AND MOTOR SPIRIT 37 

While the common grade of gasoline, heavy gasoline, used to 
have a density of about 72° to 74°B., it now commonly has 
a density considerably greater, from 56 °B. to 64°B. (see 
Art. 31). This heavier gasoline does not work so well in 
automobiles during cold weather and manufacturers have 
been obliged to modify their engines so that they could burn 
the grade of gasoline obtainable. 

41. Manufacture of Gasoline from Natural Gas. — In the 
vicinity of petroleum wells the atmosphere is charged with 
the odor of escaping gases. A considerable portion of the 
flow from an oil well evaporates immediately at the tempera- 
tare of the atmosphere. This is natural gas. Recently it 
has been found possible to change this escaping gas into an 
oil closely resembling gasoline. This is done by placing the 
gas under very high pressure and at the same time cooling it 
to a very low temperature. In 1911 there were 176 plants 
in the United States for changing natural gas from petroleum 
wells into gasoline and over 7,400,000 gal. were produced; in 
1917 there were 886 plants which produced 218,000,000 gal. 

42. Manufacture of Motor Spirit, or Motor Oil. — During 
recent years oil refiners have been constantly searching for 
some method by which they could profitably produce more 
gasoline from a barrel of petroleum. In 1911 W. M. Burton, 
a chemist in the employ of the Standard Oil Company of 
Indiana, perfected a process of producing a good substitute 
for gasoline from the residue of petroleum after the illumin- 
ating oil has been removed. This new oil is called motor 
spirit or motor oil. By a special method of "destructive" 
distillation a large amount of this motor spirit is obtained. 
In general, this "destructive" distillation is accomplished by 
distilling the residue containing the lubricating oils, the par- 
affin and the tar and coke, under high pressure and therefore 
at high temperature. 

43. Properties of Motor Spirit. — Motor spirit is somewhat 
lighter than gasoline and has somewhat different properties, 



38 



THE PRODUCTION AND USE OF LIGHT 



but it has been found to be a very good substitute for gasoline 
when used as a fuel for gasoline engines. It is said to produce 
more power per gallon than does gasoline. However, it has 
an unpleasant odor and is more inclined to produce a deposit 
of carbon in the cylinder of the engine. At the present time 
it is being used extensively only in heavy auto trucks and in 
automobiles used in business. Figure 17 shows the relative 
amounts of the products obtained from crude petroleum when 
distilled by the old methods and by the new method. 

VIII. OUR SUPPLY OF PETROLEUM 
44. The Rise of the Petroleum Industry. — Petroleum was 
first produced in commercial quantities in the United States 

in 1858. In 1860 about 2,000,000 
bbl. were produced; in 1918 about 
356,000,000 bbl. were produced. 
On the average the production of 
petroleum in the United States has 
doubled about every eight years. 
Figure 18 shows the growth of the 
petroleum industry and also shows 
the date at which each new field 
was discovered. 

45. The Oil Fields of the Uni- 
ted States. — The Pennsylvania 
fields produced all of the petroleum 
up to 1886, when the Lima, Ohio, 
field was discovered. The Indi- 
ana field was discovered in 1897; 
the Texas field, in 1901 ; the Califor- 
nia field, in 1903 ; the Oklahoma field, in 1905, and the Illinois 
field, in 1906. Figure 19 shows the best known fields of the 
United States. 

46. How Long Will Our Supply of Petroleum Last?— 
Experience has shown that the supply of oil in each field is 
limited. The Pennsylvania field is now nearly exhausted. 







Fig. 17. — Products of pe- 
troleum when distilled by 
the o]d and by the new 
methods. 



ILLUMINATING GAS LIGHTING 



39 



All the older fields are rapidly falling off in the amount of 
oil produced annually. Fortunately, up to the present time, 
as the older fields began to fail new fields have been discov- 
ered. It is thought, however, that most of the oil fields of the 
United States are now known. It seems nearly certain that 
before many years the supply of petroleum in the United 
States will be declining. Oil fields of undetermined produc- 



8 § 



c © © © 



8 S 3 S 



S g g 3 



"ill § I § § § i. 




Fig. 18. — Annual production of petroleum, 1859 to 1918. 

tiveness are known to exist in Mexico and South America 
and so it may be possible that we shall be importing much oil 
from these countries before many years. 



IX. ILLUMINATING GAS LIGHTING 

47. Illuminating Gas. — By illuminating gas we usually 
mean either manufactured coal gas or water-gas saturated 



40 



THE PRODUCTION AND USE OF LIGHT 



with oil vapors (Arts. 98 and 99). Whatever the source of 
illuminating gas, it usually is piped into the house and passes 
through a meter where its volume is measured. The price 
paid for it is usually set at a certain sum per 1000 cu. ft. 

48. The Gas Meter. — The common gas meter consists of a 
gas-tight metal case, Fig. 20, which is divided by a metal 
partition into two compartments. Each of these compart- 
ments is again divided into two compartments (A and B, 




from . Qrppnrftch 



Fig. 19.— The oil fields of the United States. 

Fig. 21) by a metal disk and leather diaphragm, D, Fig. 20. 
In the upper portion of the case is a third, gas-tight com- 
partment, VC, Fig. 20, which encloses the valves. The gas 
enters the meter at the left through the inlet pipe, I, Fig. 20. 
This inlet pipe leads across the meter to an opening in the 
floor of the valve chamber. The gas in the valve chamber is 
always under the same pressure as that in the city mains. 

Beneath each valve are three openings, or ports, Fig. 21. 
One of these ports opens into chamber A, one into chamber B, 



ILLUMINATING GAS LIGHTING 



41 



and the middle port opens into the outlet pipe, 0. When a 
gas lamp or gas stove is lighted, the pressure on the outlet is 
reduced. The disk, therefore, has unequal pressure upon its 
two sides and, as shown in Fig. 21, it is moved, in this case to 
the left. This movement of the disks is transmitted to the 
valves and to the recording mechanism. The two disks and 
the two valves keep moving back and forth as long as gas is 
being used. In a "5-Light" meter one complete vibration of 
the disks discharges about Ys or Yd of a cubic foot of gas. 

o 




Fig. 20. — 5 — Lt. consumer's meter with 
front casing, valve enclosure cover and top 
cover removed, showing- diaphragms, valves 
and gearing. 

This is the size and type of meter gen- 
erally used by gas companies to measure 
the gas supplied to the average consumer. 

Exercise 20. — To Study the Construction and Operation of a 
Gas Meter 

This exercise may be optional. A discarded meter can usually 
be secured from the local gas company, probably, if requested, with 
the casings removed as shown in Fig. 20. 



42 



THE PRODUCTION AND USE OF LIGHT 



Stand at one end of a meter from which the casing has been 
removed as shown in Fig. 20. Grasp the two flags, F. Fig. 20, one 
in each hand. By pressing the disks to right and left alternately 
you will soon learn so to operate them as to cause the crank al- 
ways to revolve in the right direction. Watch carefully the move- 
ment of the valves and the pointers. Notice that you have to press 
one disk in as far as it will go before the other disk will move in; 




Fig. 21. — This is a diagrammatic cross- 
section of a gas meter somewhat as it would 
be seen from the right side of Fig. 20. It 
shows the relation of the valve chamber, 
valves, ports and outlet pipe. Inlet to valve 
chamber is not shown. 



that after the second disk has moved in that the first disk can 
then be pulled out and that the second disk cannot be pulled out 
till the first disk has been pulled nearly completely out. One disk 
always moves just one-quarter of a vibration behind the other. 
Also notice that when one disk does move that the valve on the 
opposite side also moves so as to open the port and permit the 
gas to pass into the proper chamber, thus causing the other disk 
to move. 



ILLUMINATING GAS LIGHTING 



43 



cuae(jpFEET 

[ 8 • 2 Y 2 • 8 1(*# 2 ) 

M>5j/ MJ}?/ M>5j/ 

Fig. 22.— This meter reads 35,200 
cu. ft. 

Owe {^) feet 

Feg. 24.— What does this meter 

read ? 

(68,700) 



rilT 




Fig. 23.— This meter reads 5,700 
cu. ft. 



CiLJiicugciFirr 





Fig 25. — What does this meter 

read? 

(79,500) 



A TYPICAL GAS BILL 



John Smith, 

505 North Main St. 



Bloomington, Illinois. 
Dr. 



To the Union Gas and Electric Company ftp Gas. 



From April 25, 192 1 to May 24, 192 1 

Present Reading 



Last Reading 



Consumption of 



00 



00 



00 



cubic feet of 



at $1.48 per 1,000 cu. ft 

Discount, if paid in 10 days. 



.37 
.16 



$2.21 



This bill is due May 22, 192 1 
No discount after June 9, 192 1 



49. Reading a Gas Meter. — The small upper dial on a gas 
meter is the test dial, or proving head. It is generally used 



44 



THE PRODUCTION AND USE OF LIGHT 



only in testing the accuracy of a meter. The other dials are 
the ones ordinarily used in reading the amount of gas con- 
sumed. 

Exercise 21. — To Study the Recording Mechanism of the Gas Meter 

(Optional) 

Notice that the right-hand pointer revolves in a clockwise di- 
rection, that the second pointer revolves in a counter-clockwise 
direction and the third revolves in a clockwise direction. Study 
the gear wheels to see why this is so. 






Fig. 26. — Device 
for determining 
gas pressure. 



Fig. 27. — Automatic 
device for regulating 
gas prelbure. 



Fig. 28. — An in- 
verted illuminating 
gas lamp. 



The right-hand pointer makes one complete revolution while 
1000 cu. ft. of gas is passing through the meter; the second pointer 
makes one revolution while 10,000 cu. ft. of gas is passing through 
the meter. The left-hand pointer makes one complete revolution 
while 100,000 cu. ft. of gas passes through the meter. 

It sometimes happens that the hand or pointer is nearly over a 
figure on the dial. In Fig. 25 you cannot tell whether the left 
pointer is just past the 8 or just approaching 8. In such cases 
you have to look at the dial of the next lower denomination. 

Eead the gas meter at the school, or at home, every day for a 
week, keeping a careful record of the readings in your permanent 
notebook. 

Exercise 22. — To Measure the Pressure of Gas 

Connect a U-tube with the gas jet as shown in Fig. 26. Fill the 



ELECTRIC LIGHTING 45 

U-tube half full of water. Support the apparatus in an upright 
position. Such a piece of apparatus is called a manometer. Care- 
fully open the gas cock, letting the gas pressure into the mano- 
meter. With the ruler read accurately the difference in the level 
of the water in the two arms of the manometer. If convenient, 
permit the manometer to remain in position so that you can quickly 
determine the pressure several times each day for several days. 
Record often and record the reading together with the date and the 
hour. If the pressure varies considerably at different hours of the 
day, how do you account for it? 

50. Gas Burners. — Illuminating gas may be burned in open 
jets, "fish tail" burners, or in incandescent burners, that is, 
within mantles. In the incandescent gas lamp the gas is 
mixed with the air in a tube below the burner. This tube is 
therefore the mixer. The mixture of gas and air passes 
through a wire gauze at the top of the mixer and is burned 
within the mantle, there producing a blue, or non-luminous, 
flame but much heat. The mantle is heated white hot. It, 
therefore, glows and gives off light just as an iron poker which 
has been heated white hot glows and gives off light. All 
burners are supplied with some device for regulating the gas 
and air supply. Some burners are also supplied with an 
automatic device for regulating the gas pressure (Fig. 27). 
Recently several forms of inverted mantle gas lamps have 
come into common use (Fig. 28). 

X. ELECTRIC LIGHTING 

51. Heating Effects of the Electric Current. — Whenever 
an electric current passes along a wire, the wire becomes more 
or less heated. It may not become very hot, but it w r ould if 
it were not sufficiently large or made of the right kind of 
material to carry that amount of current. A copper wire w T ill 
carry, without becoming perceptibly heated, a current of 
electricity which would heat to a high temperature a wire of 
iron or German silver of the same size. 



46 



THE PRODUCTION AND USE OF LIGHT 



Exercise 23. — Heating a Wire by Means of an Electric Current 

Scrape the insulation off the ends of some No. 32 German silver 

jrire. Loosen the burr, or nut, on 
one of the binding posts of a 
fresh dry cell. Slip one end of 
the wire under the burr and turn 
the burr down tight upon it. Be 
certain that none of the insula- 
tion comes between the wire and 
the binding post and burr. Now 
loosen the burr on the other bind- 
ing post. Grasp the loose end of 
the wire and draw the bared por- 
tion under the burr of the sec- 
ond binding post and turn the 
burr down tight. If the cell is 
fresh, the wire will become hot; 
Fig. 29.-Electric current, fche insulation will begin to smoke 
heating a wire. and char, and probably will ac- 

tually burn. The shorter the wire, 
the hotter it will become (Fig. 29). 




p^)r//vcvi 



The over-heating of electric wires sometimes causes fires. 
If the wires in a building should be too 
small to carry the current which is sent 
over them, they may become very hot 
and set on fire the wood or other burn- 
able material with which they come in 
contact. For this reason all cities 
have very strict rules and ordinances 
governing the wiring of buildings for 
electric lighting. 

52. The Incandescent Lamp. — The 

incandescent lamp is very simple in 

principle. It consists of a glass bulb 

from which practically all the air has FlG ; 30.-lncandescent 

* "* lamp and socket, 

been removed. Sealed into the base 

of the globe are two pieces of platinum wire. The 




ELECTRIC LIGHTING 



47 



base, or top of the bulb is set by means of plaster of Paris in 
a brass base which can be screwed into a socket (Fig. 30). 
One of the platinum wires is soldered to the brass base at A, 
the other is soldered to the plate at the center of the base at 
B. "When the lamp is screwed into the socket, B comes in 
contact with B' and A is in contact with A\ completing the 
circuit. Connecting the two platinum wires within the bulb 
is a filament sometimes composed of specially prepared carbon. 
It is really a long thread of carbon. When the current passes 
through, this filament is heated to a white heat, or becomes 
incandescent (Fig. 31). There being no air present, it 
cannot burn out. If air were present it would be burned up 
in an instant. In most recent lamps the filament is made of 
a rare metal called tungsten (Fig. 32). These lamps give 
much more light with far less current than the lamps with 
the carbon filament. 

53. The Nitrogen Lamp. — As stated in the last article, in- 
candescent lamps are generally made with all air removed 
from the bulb. It is not neces- 
sary, however, to remove all of 
the air. It is only one part of 
the air which causes the filament 
to burn when heated. Air con- 
sists of oxygen and nitrogen 
chiefly. About % of the air is 
oxygen and about % of it is- nitro- 
gen. The nitrogen has no effect 
on the filament even when it is 




Fig. 32.— Tung- 
sten lamp. 



heated to white heat, at least, the Fl £ on \'~p ar ' 
nitrogen does not cause the fila- 
ment to burn up as oxygen does. In fact, it has been found 
that if all of the oxygen be removed from the bulb and the bulb 
is then filled with pure nitrogen that the light given off by the 
filament when it is heated is whiter, that more light is given 
off and that the lamp lasts longer. Most of the higher priced 
lamps, are, therefore, nitrogen filled lamps. 



48 THE PRODUCTION AND USE OF LIGHT 

54. Electric Wiring. — Electric wiring of buildings must be 
carefully done by competent electricians. As we have already 
seen, Art. 51, Exp. 23, electric wires become very hot if they 
are too small to carry the amount of current sent over them. 
It is also true that, if two wires carrying currents come 
directly into contact with each other, a spark passes between 
them. Occasionally fires are started by this "crossing" of 
"live" wires. Most electric wires are of copper and are 
covered with insulation. This insulation is a thick covering of 
material through which very little electricity passes. If the 
wires are not sufficiently large to carry the current required 
they become so hot as to destroy this insulation. Two of the 
wires upon which the insulation has been destroyed may 
come in contact, producing a spark which may set fire to the 
building. 

In the better modern buildings all electric wires are run in 
conduits. These conduits are simply iron tubes. They are 
easily bent and are placed in the walls and ceilings of the 
building when it is being constructed. When it is necessary 
to turn a corner with a conduit, as in passing from the wall 
of a room into the ceiling, care is taken to make the turn a 
curve instead of a sharp angle. When the building is nearly 
completed a long, flexible steel, resembling somewhat a long, 
straight clock spring, called a "fishing wire," is pushed 
through the conduit ; the insulated copper wire is attached to 
the end of the fishing wire and pulled into place in the con- 
duit. The placing of electric wires in conduits not only 
safeguards the building against fire, but also makes it possible 
to remove, to repair, or to replace the wiring of the building 
without injury to the walls or the decorations. 

In wiring an old building in which no conduits were placed 
when the building was constructed, the wires are "fished" 
through the walls and ceilings, the electricians working 
through small openings made in the walls, floors, or ceilings. 
Flexible insulating tubing called loom is slipped over the w T ire 
till it is completely encased before the wire is drawn into place. 



NATURAL AND ARTIFICIAL LIGHTING 49 

XI. NATURAL AND ARTIFICIAL LIGHTING 

55. Importance of Studying the Lighting Question. — 

Thinking people are rapidly coming to recognize the fact that 
more attention must be given to the lighting of our houses, 
our stores, our factories, and especially our libraries and 
schoolrooms. All who have given this matter special atten- 
tion agree that too careful consideration cannot be given this 
lighting problem in this day when we spend so large a por- 
tion of our lives in reading and studying or in other occupa- 
tions requiring close and almost constant use of the eyes. Fac- 
tory superintendents and school officials are especially active 
in endeavoring to secure better light for employees and 
students. Factory superintendents find that it pays finan- 
cially to provide the best lighting conditions possible for 
their employees. School officials and parents should give 
careful attention to securing the best of light in the school 
and the home. 

56. Light Should Come from Above. — Through ages of 
out-of-door life the eye has become adapted to receiving light 
from above. The human eye is not adapted to receiving 
strong light from below or even from a source on a level with 
the eye. By far the strongest light is received from the sun 
at midday. But at that hour the sunlight comes from over- 
head, and even its great intensity is not particularly painful. 
On the other hand, we are all familiar with the blinding* 
effect of the far less intense rays of the setting sun. "When 
boating, the rays reflected from the water come from below 
the eye; the effect is blinding and extremely unpleasant. 
Snow blindness is common in the polar regions, and even un- 
civilized races have invented devices to protect the eyes against 
the ill effects of the sun's rays reflected from the snow. Even 
the reflected light from concrete walks and from light-colored 
soils is very trying to the eyes because it comes from below. 

57. Direct Light and Diffused Light.— The most com- 
fortable light, and therefore the best, is diffused light from 



50 



THE PRODUCTION AND USE OF LIGHT 



above. When light comes directly from a luminous body it 
is said to be direct light ; when such rays are reflected from 
a smooth surface, such as a mirror or any highly polished 
surface, they still have the properties of the direct rays. All 
such rays are parallel to each other or nearly so (Fig. 33). 
All such direct light, i. e., light with parallel rays, is un- 
pleasant and more or less injurious to the eye. Light is said 
to be diffused when its rays are not parallel. 

Diffused light is usually obtained by one or the other of the 
following methods: 

First, by causing direct light to be reflected from some un- 
even or unpolished surface. Examples: (1) Light reflected 





Fig. 33.— Direct light 
reflected from a polished 
surface. 



Fig. 34.— Diffused light 
reflected from a rough 
surface. 



from a common plastered, or a "white finish" wall; (2) light 
reflected from a light-colored papered or painted wall (Fig. 
34) ; (3) light reflected from the sky, especially from the 
portion of the sky opposite the sun, in general, from the 
northern sky. 

Second, by causing the direct light to pass through some 
semi-transparent substance or ribbed or fluted glass. Ex- 
amples: (1) Light which passes through the common white or 
opalescent globes such as we use on gas mantle burners; 
(2) light which passes through the frosted tips, or "frosted 
bowl," of the common tungsten lamps; (3) light which passes 
through thin cloth such as is commonly used for curtains or 



NATURAL AXD ARTIFICIAL LIGHTING 



51 



light window shades; (4) light which passes through ribbed 
or frosted glass commonly used in skylights. 

58. Obtaining Diffused Natural Light. — Photographers 
have long recognized the value of diffused light in their work. 
Most photograph galleries are lighted by means of windows 
placed in a slanting position and facing the northern sky. 
Only diffused light from the northern sky can enter these 
windows. Further to diffuse the light, the windows are often 
fitted with ribbed glass or glass coated with a thin coat of 




Fig. 35. — Weave shed at a cotton mill, showing the saw-tooth roof. 
We are looking at the northwest corner of the building; the roof win- 
dows face the north. 



white paint. Still further to control the light, muslin cur- 
tains or light, semi-transparent shades are hung before these 
windows. 

It is becoming common practice for factories to be con- 
structed with what are known as saw-tooth roofs (Figs. 
35 and 36). The windows are placed in a slanting position 
on the north slope of the "saw-tooth" roof, thus admitting 
only diffused light from the northern sky. By this method 
of lighting, even large rooms may be evenly and effectively 



52 



THE PRODUCTION AND USE OF LIGHT 



lighted with a soft, mellow light. It is found in factories 
thus lighted, not only that the employees can do more and 
better work on account of the better light and lack of shadows, 
but also that the expense of artificial lighting is greatly 
reduced. 

School officials and schoolhouse architects are beginning to 




Fig. 36. — Interior view of the weave shed. The camera stood in the 
southwest corner of the room. Note the evenness of the lighting 
throughout the room. This room is 253 ft. by 140 ft. and contains 
648 looms. 



recognize the great value of this method of lighting. Figures 
37, 38, and 39 give three views of a schoolhouse thus lighted. 
Notice that in Fig. 39 all shades are drawn and that most 
of the light comes from above. Nearly all of the ceiling of 
the room is fitted with ribbed glass so that none but diffused 
light from above can enter. It has been found that no arti- 
ficial lighting is needed in this schoolroom during school hours 



NATURAL AND ARTIFICIAL LIGHTING 



53 



at any time during the year, although this particular school- 
house is located in northern Illinois. 

It should always be remembered that direct light produces 
a glaring effect which is unpleasant and trying to the eye, 




Fig. 37. — Exterior of an overhead lighted schoolhouse. 

(Copyright, in 11, by American Home Magazine Company, 

By courtesy of Good Housekeeping Magazine.) 




Fig. 38. — A portion of the roof of the schoolhouse. 
(Copyright, 1911, by American Home Magazine Company. 
By courtesy of Good Housekeeping Magazine.) 



while diffused light produces a soft, mellow, comfortable ef- 
fect which is not injurious. It should also be remembered 
that light should be admitted through the upper portion of 
the windows if it is impossible to admit it through skylights 



54 



THE PRODUCTION AND USE OF LIGHT 



directly above. The common practice of controlling the 
amount of light by drawing down heavy shades from the top 
of the windows is bad practice. Much better light can 
be obtained by providing each window with two" light 
shades, one for the upper and one for the lower sash of the 
window. 



HI 




i 


5 


"-■■% 




— 7-- 3 

**• 


B e ; — < m, . IB- . "f«r 



Fig. 39. — Interior view of an overhead lighted schoolroom 
Notice that the thin window shades are all drawn down. 
(Copyright, 1911, by American Home Magazine Company. 
By courtesy of Good Housekeeping Magazine.) 

59. Obtaining Diffused Artificial Light. — The first require- 
ment in all modern lighting is that the light for the room 
shall come from several sources, each of moderate intensity, 
rather than from a single source of great intensity. Figures 
40 and 41 are the floor plans of a modern residence, lighted 
by electricity. These plans indicate clearly the number and 
location of the lights as placed by an expert lighting en- 



NATURAL AND ARTIFICIAL LIGHTING 



55 



gineer. Notice that in the living room there are nine ceiling 
lights, and four wall lights — thirteen in all. In the dining 
room there are four ceiling lights and one wall light, besides 
the central canopy light. The den is lighted by five lights ; the 
hall bv three ; chanmbe'rs from three to five. 




Fig. 40. — Plan of first floor of a modern residence showing system of 
electric lighting; also other electric appliances. 



It is readily seen that, if the light for a room is thus ob- 
tained from many sources, much the same effect is produced 
as by strictly diffused light. The rays from the several dif- 
ferent sources are not parallel to each other; moreover, 
shadows are practically eliminated. The expense of operat- 
ing the many small lamps to furnish a certain amount of ilium- 



56 



THE PRODUCTION AND USE OF LIGHT 



ination is not materially different from that of operating a 
small number of large lamps giving the same amount of 
illumination. 

The second requirement of modern lighting is that the light 
shall be diffused. Lamps for use in residences, in school- 
rooms, in libraries, and even in factories, are very generally 




Fig. 41. — Second floor plan of a modern residence showing system of 
electric lighting; also other electric appliances. 

so constructed as to give only diffused light. This is especially 
true of gas and electric lighting. The gas mantle is often 
surrounded by a suitable opal glass globe; the lower portion 
of the electric light globe is frosted, while the upper portion 
is surrounded by a reflector which diffuses the light. Figure 
42 shows how the direct, parallel rays from the tungsten light 



NATURAL AND ARTIFICIAL LIGHTING 



57 



are diffused by the frosted bowl, and Fig. 43 shows how the 
direct rays from the gas mantle are diffused by the white 





Fig. 42.— Diffused light 
from the frosted bowl of a 
tungsten lamp. 



Fig. 43.— Diffused light from the 
opal glass globe of the gas mantle 
lamp. 



glass globe. In each case, the pencil of parallel rays A is 
broken up into the diffused rays a, a, a, and a, while the 
pencil of parallel rays B is 
broken up into diffused raj^s h, 
~b, ~b, and b. On the other hand 
the direct rays C pass through 
the clear glass of the upper por- 
tion of the tungsten lamp with- 
out being diffused. This direct 
light from the upper portion of 
the tungsten lamp is not per- 
mitted, however, to escape into 
the room. The lamp is sur- 
rounded by a fluted glass reflector (Fig. 44). This reflector 
reflects the larger portion of the rays as diffused light, mixing 




Fig. 44. — A fluted glass re- 
flector. Used on gas and elec- 
tric lamps. 



53 THE PRODUCTION AND USE OF LIGHT 

it with the diffused light which passes through the frosted 
bowl (Fig. 45 ray a, a, a, a, and b, b, b, b). A sufficient 




Fig. 45. — Diffused light from tungsten lamp with frosted bowl and 
fluted glass reflector. 

amount of light to illuminate the ceiling of the room passes 

through the fluted glass reflector. 
This light is also diffused, a', a', 
a', a', and V , V , b' , V , Fig. 45. 

6o. Indirect Lighting. — The 
best artificial lighting is indirect 
lighting. In the indirect system 
none of the rays from the light 
source is permitted to fall directly 
upon the surface to be illuminated. 
The lamps are placed within a re- 
flector which diffuses and reflects 
the light against the ceiling (Figs. 
46 and 47), which in turn reflects 
the light downward to the surfaces which are to be 
illuminated. The efficiency of such lighting depends 




Fig. 46. — Indirect light bowl. 



NATURAL AND ARTIFICIAL LIGHTING 



59 




Fig. 47. — A library lighted by indirect lighting. 



largely upon keeping the reflector free of dust (Fig. 
48) and upon the character and color of the ceil- 
--* ing finish. At best, however, 

not more than about 70 per 
cent, of the light is reflected by 
the ceiling; generally the effici- 
ency of the indirect systems of 
lighting is much lower than 
this. Owing to its low effici- 
ency, indirect lighting is fre- 
quently regarded as a luxury 
although its superior quality 
is recognized by everyone. 
Bright spots, such as bright, 
exposed, unshaded lights, have 
a strong tendency to cause the 
pupils of the eyes to close, thus, 
in a measure, shutting out the 
light and producing the same effect as that due to poor illum- 
ination. With indirect lighting all bright spots and glaring 




Fig. 48. — Removing the dust from 
the indirect lighting bowl. 



60 



THE PRODUCTION AND USE OF LIGHT 



effects are avoided and shadows are few; the diffused light 
coming from all parts of the ceiling makes this an ideal sys- 
tem of artificial lighting (Fig. 49). 

61. Semi-indirect Lighting. — A fairly good substitute for 
indirect lighting is the semi-indirect lightino. A semi-trans- 
parent bowl, shaped like the indirect bowl, is used. This bowl 
is smooth and polished on the inside, or upper side, so as 
to reflect some light to the ceiling. The glass used is opal 
glass or it is frosted on the lower side so as to diffuse all 
light which passes through it. 





Fig. 49. — A. A bad position and poor light. There is a bright spot 
before the eye and the light is reflected from the book to the eye. 
B. A good position and good light. The light reflected from the ceil- 
ing is diffused light. 

62. Amount of Light Which Should be Provided. — It is 
impossible to give any but very general rules governing the 
amount of light which should be provided for a room, and 
therefore the number and size of the lamps which should be 
installed. The color and the nature of the wall coverings 
and the character of the furniture and the decorations, as 
well as the use to which the room is to be put, all have im- 
portant bearings upon the lighting. A white wall paper or a 
" white finish" wall will reflect 80 per cent, of the light; 
a red, dark brown, or dark green wall will reflect only about 
15 per cent. A light buff or yellow wall will reflect 45 per 



NATURAL AND ARTIFICIAL LIGHTING 



61 



cent, of the light; a light apple green will reflect about 40 
per cent. The decorations of a room determine largely the 
illumination of the room with a given amount of lighting. 

63. Controlling the Distribution of Light. — It is probable 
that fully 50 per cent, of the light produced in ordinary resi- 




H — L-^U ^ 1 — \1 f r ~ 

Tv/r 80 \va/\ 



Fig. 50. — Upright gas 
mantle lamp. 



Fig. 51.— The distribution 
curve for the lamp. 





Fig. 52. — A reflex or inverted gas mantle 
lamp with prismatic glass reflector. 



Fig. 53.— The distribution 
curve for the lamp. 



dence lighting is wasted. Light is wasted unless it is used to 
illuminate the surfaces which need to be illuminated. When 
reading a book or paper, a person needs to have that page 
illuminated ; it is of no benefit to the reader, -however, to have 
the walls and ceiling of the room illuminated to the same 
extent. In fact, if all other objects in the room were ilium- 



62 THE PRODUCTION AND USE OF LIGHT 

inated to the same intensity as the book, they would tend 
to draw the attention of the reader from the page. We all 
know that the attention of the audience in a theater is directed 
to the players by subduing the light in the body of the house 
and increasing the light on the stage. 

In modern lighting, the choice of fixtures and shades is 
determined by the use to be made of the light. If the pur- 
pose is to supply light for the general illumination of the 
room, the fixtures and shades will be chosen which will dish 
tribute the light with approximately equal intensity in all 
directions, Figs. 50 and 51. If, on the other hand, it is 
desired to illuminate a desk or table standing directly be- 
neath the lamp, another style of fixture and shade should be 
used, Figs. 52 and 53. 

During recent years manufacturers of lighting fixtures for 
both gas and electric lighting furnish the dealer with elab- 
orately illustrated catalogues showing the exact distribution 
of light from each fixture they make. An intelligent pur- 
chaser can, therefore, today choose a fixture exactly suited to 
furnish the amount and quality of light desired and have that 
light directed to the point, or points, where it is needed. 

64. Relative Cost of Operating Gas and Electric Lights. — 
Illuminating gas is furnished to the consumer under very 
slight pressure. The price charged varies in different local- 
ities but usually ranges between 80 cents and $1.50 per 
1000 cu. ft. 

Gas may be burned either in the open flame jet or in the 
welsbach mantle. The open flame jet, or fish tail burner, 
usually burns about 5 cu. ft. of gas per hour. If gas costs 
$1.00 per 1000 cu. ft. the cost per hour for gas is about 5 
mills for an open flame jet. 

When gas is burned in a Welsbach mantle it is generally 
consumed at the rate of from 3% to 5 cu. ft. per hour. The 
cost for gas, is, therefore, from 3% to 5 mills per hour. 

Electricity is sold by the watt-hour or kilowatt-hour. 
The kilowatt-hour is equal to 1000 watt-hours. The ordinary 



NATURAL AND ARTIFICIAL LIGHTING 63 

house meter reads off directly the number of kilowatt-hours of 
current used. This watt hour-meter, or "watt-meter," as 
it is usually but erroneously called, is really little more than 
a very small and easy running motor (Fig. 54). A very 
small portion of the current passing through this meter runs 
the motor which, in turn, operates a chain of gear wheels 
which turn the hands before the dials (Fig. 54). The usual 
cost of electric current for lighting purposes is from 8 to 
15 cents per kilowatt-hour. 




Fig. 54. — A watt-hour meter 

The common carbon filament lamps are made in several 
sizes; the sizes most commonly used are the 50-watt lamp 
and the 100-watt lamp. If electricity sells for 10 cents per 
kilowatt -hour, the current for the 50-watt lamp costs 5 mills 
per hour; the current for the 100-watt lamp costs 10 mills, or 
1 cent per hour. 

The tungsten filament lamp is also made in several sizes ; 
the sizes most commonly used for resident lighting are the 
25-watt lamp, the 40-watt lamp, and the 60-watt lamp. There- 
fore, at 10 cents per kilowatt-hour for current, these lamps 



64 



THE PRODUCTION AND USE OF LIGHT 



cost about 2y 2 mills, 4 mills, and 6 mills, respectively, per 
hour. 

Exercise 24.— Reading the Common House Kilowatt-hour Meter 

Study carefully the dial of a watt-hour meter and see how it 
differs from the dial of the gas meter, Figs. 22, 23, 24 and 25. 
Notice that the number of cubic feet indicated above each dial on 
the gas meter shows the amount of gas used while the pointer has 
made one complete revolution. This is not true of the numbers above 
the dials on a watt-hour meter. The numbers on the watt-hour 
meter indicate the number of watt-hours of electrical energy used 
while the pointer is passing over one of the ten spaces on the dial. 



KILOWATT -HOURS 
One Division of Is Dial = 1 K.W. Hour 



Fig. 55. This dial reads 1581 
k.w. hrs. 



100 VOLTS 
10s Is 




KILOWATT -HOURS 
One Division of Is Dial = 1 K.W. Hour 



Fig. 56. — This dial reads 2775 
k.w. hrs. 



5 AMPERES 
\QQO s 100* 



100 VOLTS 
10« Is 




KILOWATT -HOURS 
One Division of Is Dial = 1 K.W. Hour 

Fig. 57. — What does this dial 
read? (5665) 



KILOWATT -HOURS 
One Division of Is Dial = 1 K.W. Hour 



Fig. 58.— What does this dial 
read? (8909) 



If electric current costs 10 cents per kilowatt-hour, what was the 
cost of the current used between the reading of Fig. 55 and Fig. 56? 
Between the reading of Fig. 56 and Fig. 57? Between the reading 
of Fig. 57 and 58? 

Although it is probably, as yet, somewhat more expensive 
to produce a certain amount of light using electric current 
and tungsten lamps than it is using gas and Welsbach mantle 
burners, still electric lighting affords so many advantages that 



NATURAL AND ARTIFICIAL LIGHTING 65 

it is rapidly displacing gas where both are available. Some 
of these advantages are: (1) Greater convenience; (2) 
smaller and more numerous units are easily provided — a very 
desirable feature; (3) to a certain extent gas lights consume 
the oxygen in the air and give carbon dioxid ; electric 
lights do not; (4) to a certain extent gas lights tend to 
blacken the ceiling and walls of the room; electric lights do 
not; (5) while gas may be put to many uses other than 
lighting in the home, notably cooking and heating, modern 
invention makes it possible to use the electric current in the 
home in a multitude of ways (Figs. 40 and 41). 



CHAPTER II 
THE PRODUCTION AND USE OP HEAT 

I. THE BEGINNING OF WARMTH AND COMFORT 

65. Importance of Fire. — Wood has been burned by man 
ever since the beginning of history. It is impossible even to 
guess at the time when it was first used as fuel by our ances- 
tors, although there undoubtedly was a time when man did 
not know the use of fire. 

We are so accustomed to fire that we can scarcely realize 
how much we are indebted to it for the necessities and com- 
forts of life. We forget that, if all the fires in the land 
should go out, nearly all of the work we see being done about 
us would cease; that all travel would stop; that, with the 
coming of darkness all play and pleasure, reading and work 
would come to an end. We forget that, if we had no fires, 
we could have no houses to live in, no school buildings to 
study in ; that there would be no street cars, no railroads, no 
clocks, no watches, no pocket knives — indeed we can hardly 
mention anything which we enjoy today that we could then 
have except the fruits, the grains, and the vegetables that 
grow from the soil. Even then, we should have no tools with 
which to cultivate the land except such as could be shaped 
from limbs of trees or from rocks. We should soon all 
be savages and again live in the woods, sheltered only by rude 
huts. Our food would be raw meat and such roots, berries, 
and fruits as we could find. 

66. Fires 100 Years Ago. — At the beginning of the 19th 
century, wood was cheap and labor scarce, and the big fire- 
place commonly served for both cooking and heating. Hinged 
to the jamb of the fireplace was an iron crane filled with 
dangling pot-hooks. It was pulled out so that pots and 
kettles might be hung upon the hooks, and the crane was 

66 



THE BEGINNING OF WARMTH AND COMFORT 



67 



then hung back over the blazing fire. Potatoes were baked 
in the hot ashes. In the wall beside the fireplace was built 
the brick oven, with its flat bottom and arched top, having 
an iron door in front (Fig. 59). On baking day, a wood fire 
was built in the oven, and when it had burned to coals and 
thoroughly heated the oven, the fire was neatly removed and 




Fig. 59. — An old-fashioned fireplace and oven. (From Stories' of Useful 
Inventions. By permission of The Century Company.) 

the bread placed on the oven bottom. In those days, there 
was usually no attempt to heat other than the living room of 
the house. The sleeping rooms, in the winter, were damp and 
bitter cold. The bedstead was surrounded by thick, heavy, 
bed curtains that hung from the bed frame which reached 
nearly to the ceiling. Before retiring, the sheets were warmed 
by means of a warming pan. This consisted of a metal pan 



68 THE PRODUCTION AND USE OF HEAT 

mounted on a handle and having a cover. Live coals were 
placed in the pan and it was then moved about between the 
sheets till the chill and the dampness were removed. 

In the living room in Whittier's old home, at Haverhill, 
Massachusetts, can be seen today the fireplace and its old 
andirons upon which once rested the blazing logs. The crane 
fastened to the left-hand jamb supports numerous pot-hooks 
and pots. Two pairs of tongs lean against the jambs. In 
the wall at the right is the oven with its iron door. Hanging 
at the left of the fireplace is the warming pan and the lantern. 
The latter consists merely of a tin can with many small holes 
punched in its sides and a socket within to hold the candle 
upright. On the floor beneath them is the foot-warmer. Be- 
yond the door is the flax wheel and the desk at which Whittier 
wrote all of his earlier poems. The candlesticks and candles 
are on the desk. 

"And for the winter fireside meet, 
Between the andiron's straddling feet, 
The mug of eider simmered slow, 
The apples sputtered in a row." 

This old living room has been restored till it accurately 
represents the home conditions in which the Quaker poet lived 
and wrote his earlier poems. 

For two centuries after the landing of the Pilgrims the 
people of New England shivered throughout the long, bleak 
New England winters. Most of the colonists had come from 
much milder climates and the icy blasts which met them were 
most trying. In many instances the suffering was intense. 
In the first place, many of the houses were not well con- 
structed and the cold wind would creep in. In the second 
place, the huge fireplaces but poorly heated the one room which 
was supposed to be warmed. Even though Whittier wrote : 

''What matter how the night behaved! 
What matter how the north wind raved! 
Blow high, blow low, not all its snow 
Could quench our hearth-fire's ruddy glow," 



THE BEGINNING OF WARMTH AND COMFORT 69 

it still was true that a short distance from the fireplace the 
room was so cold as to be quite unendurable to us today. 
There are plenty of records to show that it was not uncommon 
for ink to freeze upon the pen even as the recorder wrote his 
diary at the chimney side. "One noted, that when a great 
fire was built upon the hearth, the sap which was forced out 
of the wood by the flames froze into ice at the ends of the 
logs." "President John Adams so dreaded the bleak New 




Fig. 60. — A winter's service at church. 

(Copyright, 1900, by Curtis Publishing Company, and reproduced 

by courtesy of the Ladies' Home Journal.) 

England winter and the ill-warmed houses that he longed to 
sleep like a dormouse every year, from autumn to spring. " 
(Home Life in Colonial Days, Earle.) 

All through the days of the colonies and for a half century 
following the Revolutionary War, the churches of New Eng- 
land were entirely without heat. The men sat throughout 
the % long forenoon and afternoon services wrapped in over- 
coats and wearing their warmest mittens and footwear. The 



70 THE PRODUCTION AND USE OF HEAT 

women and children were provided with foot warmers, sheet- 
iron boxes containing live coals (Fig. 60). 

67. The First Stove. — The first stoves ever used by our 
American forefathers were made about 40 or 50 years before 
the Revolutionary War. The stove was merely a cast-iron 
box with a door in one end and an opening in the upper side 
through which the smoke could escape. The back or side of 
the fireplace was removed and this box was slipped into the 
space beneath the chimney. A very peculiar thing about this 
stove, as it seems to us, is the fact that the end containing 
the door was left on the outside of the house. What we should 
call the back of the stove projected into the room and the 
operator was obliged to go out of the room into the wood 
house to feed it. It was, however, a great improvement over 
the open fireplace because it overcame the strong draft, 
which, in the open fireplace, sent most of the heat up and 
out of the chimney. 

68. Franklin's Stove. — In 1742 Benjamin Franklin invented 
his ' ' Pennsylvania Fireplace." He called it "an open stove 
for the better warming of a room." It was really an open 
stove which was placed within the old fireplace. The air of 
the room became heated when it came in contact with any 
portion of the stove. Franklin said: "The use of these fire- 
places in very many houses, both in this and neighboring 
colonies, has been and is a great saving of wood to the in- 
habitants. Some say it saves five-sixths, some say three- 
fourths, others much less. I suppose two-thirds or one-half 
is saved ; my -room is twice as warm with one-fourth the wood 
formerly used. " 

As a means of securing comfort, Franklin 's invention, with- 
out doubt, was the greatest single step ever made in perfecting 
heating devices. With this stove it became possible to heat 
most of the rooms of a house so that they were fairly com- 
fortable. Such stoves would hardly be considered of great 
value today for heating purposes, but at the time of .the 
Revolutionary War they were the kings of heaters. In fact, 



THE CHEMISTRY OF FIRE 71 

there was no very great improvement over the Franklin stove 
for a century. In this line of advancement, as well as in 
many other lines, the world must ever recognize in Benjamin 
Franklin one of its greatest benefactors. 

Today we have heating devices much more complicated than 
Franklin's stove. These include, beside the improved and 
modern stove, the warm air furnace, steam and hot water 
heater's, gas heaters, and electric heaters. These modern heat- 
ing devices require much less attention and insure greater 
comfort to the inhabitants of the house than did Franklin 's 
stove. All of these heating arrangements, mentioned above, 
with the exception of the electric heater, make direct use of 
fire for the production of heat, hence it is fitting that just 
here we study what goes on in a fire and how it may be 
controlled. 

II. THE CHEMISTRY OF FIRE 

69. Fire was a Riddle to the Ancients. — Fire was long a 
riddle to the ancients, and even to people of more recent 
times. It was not until after the close of the Revolutionary 
War that the true explanation of fire was brought out by 
Lavoisier (La-vwa-zya/) a French chemist. His explanation 
was (1) that the fuel which is burned is composed of certain 
fuel elements, namely, carbon and hydrogen; (2) that the air 
contains a third element called oxygen; (3) that burning con- 
sists of the chemical union of the fuel elements, carbon and 
hydrogen, with the oxygen of the air; and (4) that this com- 
bination of carbon and hydrogen with oxygen produces heat 
and light. This explanation of fire by Lavoisier is still ac- 
cepted today. 

This explanation immediately calls for further explana- 
tions of what is meant by "chemical element," "chemical 
union," "fuel elements," "oxygen," "carbon," and "hydro- 
gen." These will be discussed in turn next. 

70. Chemical Elements. — Carbon is called a chemical 
element because no other kind of matter has yet been ob- 



72 



THE PRODUCTION AND USE OF HEAT 



tained from it alone. Carbon, alone, can produce only carbon. 
So it is with oxygen and with hydrogen. Substances that 
have, so far, defied all attempts on the part of man to change 
them into simpler substances are called chemical elements. 
About 80 chemical elements are known. The following is a 
list of the common chemical elements. 



Aluminum 


Hydrogen 


Nickel 


Sik'er 


Calcium 


Iron 


Nitrogen 


Sodium 


Carbon 


Iodine 


Oxygen 


Sulphur 


Chlorine 


Lead 


Phosphorus 


Tin 


Copper 


Magnesium 


Potassium 


Tungsten 


Gold 


Mercury 


Silicon 


Zirus 



It is from the chemical elements, in various combinations, 
that the many, many different substances known on the earth 
are derived. 

71. Chemical Union. — This is the process by which the dif- 
ferent chemical elements, or the compounds derived from 
them go together to make various combinations called chemi- 
cal compounds. Chemical union resulting in the formation 
of a chemical compound is illustrated in the following exer- 
cise using the elements copper and sulphur. 



Exercise 25. — Union of Elements to Form Compounds 

Clean a piece of copper foil with emery or sand paper until the 
surface of the metal is bright. What is the color of the copper? 
Now hold the cleaned foil with a pair of tongs and sprinkle a thin 
layer of powdered sulphur on the surface of the copper. What is 
the color of the sulphur? Are the substances copper and sulphur 
elements or compounds? (See Art. 70, list of chemical elements.) 
The copper and sulphur are undergoing chemical change at or- 
dinary temperatures, but very slowly. The rate of union may be 
increased by heating them. By means of the tongs hold the copper 
and sulphur in the flame of the burner and watch changes. If too 
much sulphur has been used, it may be burned off from the surface 
of the metal. Remove the foil from the flame and examine the 
surface of the copper. What is its color now? This is a new 
substance produced by the union of the rcopper and the sulphur. 
It is known as copper sulphid. Possibly not all of the copper was 



THE CHEMISTRY OF FIRE 73 

used in the change. Only that portion on the outside, and next to 
the sulphur really underwent chemical change. Heat was liberated 
as the elements united but it was not noticeable in the flame. 

72. Discussion of the Exercise. — This experiment illus- 
trates chemical union. The pair of elements, copper and 
sulphur, illustrate many such pairs that might be made to go 
into chemical union. Thus copper and oxygen combine to 
form copper oxid, carbon and oxygen unite and form carbon 
dioxid, silicon and oxygen make silicon dioxid, or sand, 
sodium and chlorine will combine to make sodium chlorid, or 
common salt. The number of such combinations of two, and 
even more than two, elements to form compounds is very 
large indeed. It is the compounds resulting from such com- 
binations of which the earth and the things thereon are made. 

The student should be careful not to confuse chemical com- 
pounds with mixtures. The making of a chemical compound 
involves a much deeper process than making a mixture. When 
two elements are merely mixed, each of the elements, if they 
are solids, not liquids or gases, may still be seen, if not with the 
eye, then with the aid of a microscope. We may mix, for in- 
stance, powdered copper and powdered sulphur, and a careful 
examination will still show copper particles and sulphur 
particles. But when we cause the two to unite chemically 
we have a substance, called copper sulphid, in which no 
amount of examination will show any copper or sulphur. 
Copper and sulphur, as such, have disappeared and they have 
been merged into one substance, copper sulphid, which is some- 
thing entirely different from the elements of which it is made. 
So it is with all compounds with reference to the elements 
from which they are made. Moreover, a chemical compound 
always contains a certain percentage of each of the elements 
composing it, whereas a mixture may contain the elements in 
varying percentages. 

73. Fuel Elements. — These are the chemical elements com- 
monly found in fuels and upon which the fuel depends for its 
ability to burn. These fuel elements are carbon and hydro- 



74 THE PRODUCTION AND USE OF HEAT 

gen. While there are many forms of fuel, such as solid fuels, 
including wood and coal ; and liquid fuels like kerosene, gaso- 
line, and alcohol; and gaseous fuels such as coal gas, gasoline 
gas, and other gases, it is found that the ability of these fuels 
to burn is dependent on the presence of one or both of the 
fuel elements, carbon and hydrogen. 

We shall next study carbon and hydrogen, together with the 
oxygen upon which the burning of the fuels depends. 

74. Carbon. — This is a solid, black in color except in case 
of the diamond which is crystallized carbon. Charcoal is 
composed chiefly of carbon, while the so-called lead of the 
lead pencil is a mixture of a form of carbon, called graphite, 
and clay. 

75. Oxygen. — This is a colorless gas. It is one of the con- 
stituents of the air. The other chief constituent of the air 
is another gas called nitrogen. It will be remembered that 
nitrogen, as well as oxygen, is a chemical element (Art. 70). 
These gases are mixed together in the air. They are not in 
chemical union. The air also contains the compounds carbon 
dioxid and water vapor, both of which are colorless gases. 
The following table gives the constituents of the air out of 
doors. 

Oxygen, 21 volumes in 100 volumes of dry air. 
Nitrogen, 78 volumes in 100 volumes of dry air. 
Water vapor, variable within wide limits. 
Carbon dioxid, 3 volumes in 10,000 volumes of dry air. 

Now the burning of fuels requires oxygen and produces car- 
bon dioxid and water vapor. It is evident then, that combus- 
tion will tend to change the proportions of the constituents 
of the air. Why the oxygen is not all used up and why the 
volume of the carbon dioxid does not largely increase in 
amount will be explained in Arts. 310 and 374. 

Since oxygen is commonly found mixed with the other sub- 
stances in the air we wish to get it in a pure, or nearly pure, 
form so that it may be studied better. There are many 



THE CHEMISTRY OF FIRE 



75 



compounds of oxygen which may be made to give up a 
part or all of their oxygen by heating or by other means. 
One such compound is potassium chlorate, a white crystalline 
compound composed of potassium, chlorine, and oxygen. 
When it is heated, it liberates its oxygen. If it is mixed with 
manganese dioxid, it liberates oxygen at a much lower tem- 
perature. 

Exercise 26. — The Preparation and Properties of Oxygen 

Set up the apparatus as shown in Fig. 61. Remove the test tube, 
fill it about one-tbird full of potassium chlorate; then place about 
an equal amount of manganese dioxid in the tube. Close the tube 
with the hand and shake it until the chlorate and the dioxid are 
well mixed. Replace the stopper in the apparatus, making sure 




Fig. 61. — The preparation of oxygen. Potassium chlorate and man- 
ganese dioxid are placed in the test-tube and heated and the oxygen is 
collected in bottles. Be careful to see that the delivery tube extends 
entirely through the rubber stopper. Do not allow the delivery tube 
to become clogged. 

that the stopper fits tightly. Apply gentle heat to the mixture in 
the tube, beginning at the end which has the stopper, but do not 
heat the stopper, for it may catch fire and make serious trouble. 
As the oxygen is given off, gradually and carefully extend the heat 
toward the closed end of the tube. At no time should so much 
heat be applied that the escaping gas carries the oxygen-producing 



76 THE PRODUCTION AND USE OF HEAT 

mixture along with it bodily, thus tending to clog the delivery tube 
and to prevent the escape of the gas. Fill wide-mouthed bottles with 
the gas produced. To do this, submerge the bottle in the 
water in the pan, seeing that all of the air is expelled from the 
bottle by the water; then, keeping the mouth of the bottle beneath 
the surface of the water, invert the bottle and place it over the end 
of the delivery tube. As the oxygen escapes from the delivery 
tube, it bubbles into the bottle of water and crowds the water out. 
When the first bottle is full, place another bottle over the end 
of the delivery tube just as the first one was placed. Set the full 
bottles on the top of the table, keeping them inverted. The water 
around the mouth of the bottle will keep the oxygen from getting 
out. When you have driven as much oxygen as possible from the 
mixture in the tube, remove the end of the delivery tube from the 
water; then remove the flame from the test tube. 
Study the oxygen obtained as follows: 

(a) Effect of Pure Oxygen on a Burning Splinter. — Place a splin- 
ter of wood in a bottle of oxygen to see that the wood does not 
burn in oxygen at ordinary temperatures. Now heat the splinter, 
that is, "set it on fire," and thrust it into a bottle of oxygen. What 
is the result? In which, gas, oxygen or air, does the wood burn 
more rapidly? Why? Ignite another splinter and blow out the 
flame leaving the splinter merely glowing. Hold it in the air for 
a moment to see whether it will again burst into a flame. If it 
does not, place the glowing splinter in a fresh bottle of oxygen and 
observe the result. How do you explain it? 

(b) Effect of Pure Oxygen on Smoldering Substances. — Repeat 
the latter part of (a) using a piece of smoldering candle wicking 
or a piece of burning punk and -a fresh bottle of oxygen. 

(c) Effect of Pure Oxygen on Glowing Charcoal. — Wrap a small 
wire around a piece of charcoal the size of a lead pencil and an 
inch in length. Heat the charcoal in the flame until it glows. 
Quickly lower it into another bottle of oxygen and notice what 
takes place. When the charcoal ceases to burn, remove it from 
the bottle and close the mouth of the bottle. Compare the rate 
at which the charcoal burns in the oxygen with that in the air. 
Charcoal is chiefly carbon, and the compound resulting is carbon 
dioxid, a gas, which remains in the bottle. Caution. — Quench the 
charcoal by putting it into water. If left burning it might set 
the building on fire. 

(d) Effect of Pure Oxygen on a Burning Candle. — Twist a small 
wire around a short piece of candle or taper, light the candle and 
observe the rate at which it burns in the air; then plunge it into a 






THE CHEMISTRY OF FIRE 77 

fresh bottle of oxygen. Observe the rate of burning in the oxygen. 

(e) Burning Iron in Oxygen. — Slightly unravel the end of a piece 
of iron picture wire. Heat the unraveled end in the flame; then 
quickly dip it into a little powdered sulphur and at once plunge it 
into a bottle of oxygen. Does the iron bum? It may be necessary 
to make several trials before the iron burns brilliantly. Do not use 
too much sulphur, just enough to kindle the iron. Can you make 
iron burn in the air? 

(/) The Limewater Test for Carbon Dioxid. — Place a tablespoon- 
ful of fresh, clear limewater in each of the bottles used above. 
Place the palm of the hand over the mouth of each bottle in turn 
and shake well. In which case does the limewater become milky in 
color and in which does it not? There may be several dark-colored 
specks in some of the bottles, but disregard them. The milky color 
of the limewater is a test for carbon dioxid. 

76. Discussion of the Experiment. — The union of oxygen 
with the substances burned in this experiment is termed 
oxidation. The products arising from the union of the 
oxygen with the elements burned are called oxids. Thus 
the carbon in the wood, candle wicking, charcoal, and candle 
united with the oxygen to form carbon dioxid. The hydrogen 
in the wood, the candle wicking, and the candle united with 
the oxygen to form water. This was in the form of steam 
when made. The iron of the picture wire formed iron oxid. 

Carbon dioxid causes limewater to become milky. Oxygen 
does not change limewater. 

77. Temperature and Oxidation. — A factor which in- 
fluences the rate of oxidation is temperature. At ordinary 
temperatures the rate of oxidation is very slow for most 
materials. Wood and many other fuel materials decay at 
ordinary temperatures. They are really undergoing what is 
called slow oxidation. At higher temperatures the rate is 
much more rapid. For each substance that burns, there is 
a temperature at which it burns rapidly in the air. This 
temperature is called the kindling temperature. When a 
fire is kindled, the aim is to heat the fuel to be burned by 
burning the kindling, the kindling having a lower kindling 
temperature than the fuel. Thus sulphur is used to kindle 



78 



THE PRODUCTION AND USE OF HEAT 



the iron; kerosene, paper, or shavings are used to kindle the 
coal or wood because these kindling agents have lower kin- 
dling temperatures than the fuel which is to be burned. When 
the fuel is once ignited, it then liberates heat fast enough to 
keep itself at the kinding temperature and so the fire continues 
as long as the concentration of the oxygen is sufficient. Wet 
fuels often require so much heat to dry them that the burn- 
ing portion can not supply heat enough to dry the unburned 
portion and to raise it to the kindling temperature. Hence 



Thistle Tube 



■Burette Cterry> 




Fig. 62 — Apparatus for generating hydrogen. 

the fire goes out. Water is thrown on a fire to cool the burn- 
ing material below its kindling temperature. Also the steam 
arising from the water serves to dilute the air and thus to 
lower the concentration of the oxygen so that the fire goes out. 
78. Study of Hydrogen. — Hydrogen is the second of the 
fuel elements. It is to be prepared and studied. 



Exercise 27. — The Preparation and Properties of Hydrogen 

Set up the apparatus as shown in Fig. 62. Cover the bottom of 
the flask with granular zinc, replace the stopper and see that all 
joints of the apparatus are tight. Prepare to collect the gas, 



THE CHEMISTRY OF FIRE 79 

hydrogen, just as oxygen was collected. Do not have any flames 
closer than 4 ft. from the hydrogen generator. Pour water down 
the thistle tube until the bottom of the flask is well covered and 
the lower end of the thistle tube is submerged; then pour in con- 
centrated hydrochloric acid slowly until the action between the 
zinc and the acid is rapid. Do not spill the acid on the hands, 
clothing, or desk. Allow the hydrogen to escape from the delivery 
tube for about one minute; then collect the gas over water in wide- 
mouthed bottles. Fill one bottle half full of the gas. Finally remove 
the delivery tube from the water, wipe it dry, and allow the gas to 
flow into a dry bottle containing air. Cover this bottle* as well as 
possible. Take the hydrogen generator apart, fill the flask with 
water to dilute the acid and stop the action. Pour the dilute acid 
into the sink, rinse the unused zinc with fresh water and save the 
metal for future use. 

Study the hydrogen as follows: 

(a) The Burning of Hydrogen. — Light a splinter of wood. Lift 
one of the full bottles of hydrogen from the water, and, keeping the 
mouth of the bottle down, bring the flame of the splinter to the 
mouth of the bottle. Pay no attention to the noise, but look for 
the flame of burning hydrogen playing about the mouth of the 
bottle where it is uniting with the oxygen of the air. The experi- 
ment may be repeated with other bottles of the gas. 

(b) The Burning of a Mixture of Hydrogen and Air. — Prepare 
another burning splinter. Lift from the water the bottle which was 
filled half full of hydrogen, keeping the mouth of the bottle down. 
What enters the bottle as the water runs out? Allow the air and 
hydrogen a few seconds in which to mix ; then ignite them by means 
of the flame. The result illustrates the burning of a mixture of 
hydrogen and air. The noise is due to the sudden rush of the 
products of the burning from the bottle. The outrush is due to 
the heat generated by the combustion. Such a mixture is said to 
be explosive. Such mixtures should be ignited only in bottles 
having wide mouths to allow the easy escape of the products of 
the burning. 

(c) The Product Formed When Hydrogen Burns in Air. — Pre- 
pare another burning splinter of wood. Take the dry bottle con- 
taining the mixture of air and hydrogen, and keeping it mouth 
downward, ignite the mixture. After the combustion is over care- 
fully examine the inside of the bottle. Do you find any moisture 
on the walls? Where did this come from? What then is the 
product arising from the burning of hydrogen in air? Why was it 
necessary to use a dry bottle for this part of the experiment? 



80 THE PRODUCTION AND USE OF HEAT 

79. Discussion of the Exercise. — When hydrogen burns, it 
unites with oxygen, liberating much heat and producing water, 
in the form of vapor, as a product. This vapor condenses to 
water when it is cooled. Hydrogen is the lightest known 
substance. It is much lighter than air, and hence the bottles 
containing hydrogen are kept inverted so that the hydrogen 
will not run out. Mixtures of hydrogen and air containng 
more than 5 per cent, by volume of hydrogen and less than 
72 per cent, are explosive. That is to say, a mixture of 95 
cu. ft. of air and 5 cu. ft. of hydrogen will explode; so will 
other mixtures containing relatively less air and more hydro- 
gen until a mixture of 28 cu. ft of air and 72 cu. ft. of hydro- 
gen is obtained, beyond which the mixture is no longer 
explosive. 

80. Hydrocarbons. — 

Exercise 28. — Burning Compounds of Hydrogen and Carbon 

(a) Light the Bunsen burner and hold over the flame an inverted, 
dry, cold tumbler. What substance appears on the inside of the 
glass? Pour a tablespoonful of limewater into the tumbler, cover it 
and shake it. Notice the change in the limewater. What two sub- 
stances were formed by burning the gas? 

(b) Repeat (a) but use a candle flame instead of the gas flame. 
Study the products arising from the burning of the candle. 

(c) Repeat (a) using a kerosene lamp flame, studying the prod- 
ucts of the combustion. 

What products of combustion may we expect when fuels con- 
taining hydrogen and carbon are burned? 

Hydrocarbons are compounds of hydrogen and carbon. 
Petroleum is a very complex mixture of hydrocarbons. Some 
of the hydrocarbons of petroleum are gases at ordinary tem- 
perature, some are liquids, and some are solids (Chap. I, 
Sec. IV). The liquids form the largest portion. By dis- 
tillation, the gaseous, liquid, and solid hydrocarbons are 
separated. Gasoline and kerosene are common liquid hydro- 
carbons, while the paraffin of which the candle is made is a 
solid hydrocarbon. There are not large amounts of uncom- 



THE CHEMISTRY OF FIRE 81 

bined hydrogen in nature, but the compounds of hydrogen and 
carbon known as hydrocarbons are abundant, and in these, 
the hydrogen and carbon are combustible. 

81. The Burning of Fuels Produces Energy. — It is well 
known to everybody that heat is produced when a fuel burns. 
Now heat is one of the forms of energy. "Energy is work or 
anything that may arise from work \or oe converted into 
workJ' We readily see then, that heat is energy because we 
have seen heat doing work in pulling the train or running the 
automobile. The locomotive of the train or the engine of the 
automobile is the machine in which heat is produced and con- 
verted into work. Electricity is another form of energy. It 
may do work for us or it may produce light or heat. Fuels 
possess a kind of energy called chemical energy, because the 
energy is set free when the fuel undergoes a chemical change 
called burning. In this ability of fuels to burn and liberate 
energy we find the real reason for burning them. We may 
want the energy in the form of heat to warm our houses or to 
cook our food. We may want the energy of the fuel to do 
work for us by pulling the train or running the automobile. 
Now we can begin to see why it was said at the first chapter 
that to take fire away from man would soon cause him to be- 
come a savage having no machinery, tools, nor implements, 
and living in caves and eating his food uncooked. Thus we 
see that the discovery of fire by primitive man back some- 
time in the dim past was one of the most important discov- 
eries he ever made. It has enabled him to pass from savagery 
to civilization. 

82. Summary of Section II. The Chemistry of Fire. — (1) 
Fire is the chemical union of the oxygen of the air with the 
fuel elements, carbon and hydrogen, of the material burning. 
(2) The fuel elements and oxygen are three of the eighty or 
more known chemical elements. (3) When carbon unites with 
cxygen in the burning process a gas, carbon dioxid, is formed, 
while hydrogen uniting with oxygen produces water vapor, 
another gas. These two gases, carbon dioxid and water vapor, 



82 



THE PRODUCTION AND USE OF HEAT 



are the common gaseous products arising from fire. (4) In 
order that oxygen may unite with the fuel elements the tem- 
perature of the fuel must be at least as high as a certain tem- 
perature called the kindling temperature. (5) When the fuel 
burns it produces energy which appears as heat or light. 
Man has learned to put this energy to various uses to serve his 
purpose. 

III. BURNING OF WOOD AND COAL 

83. The Burning of Wood. — Wood is composed chiefly of 
carbon, hydrogen, and oxygen. These elements are present 
in various compounds which make up the wood. When the 







Fig 63. — Burning wood 
on gauze. 




xisaasx st^w*- 



Fig. 64. — Distillation of wood. 



wood is heated to the kindling temperature in the presence of 
the air containing oxygen, a complicated series of changes 
take place which may be understood in part at least, by 
means of Exs. 29 and 30. 



Exercise 29. — Heating Wood in the Air 

Place two or tbree thicknesses of wire gaiize on a ring attached to 
a ring stand and lav a piece of wood about V 2 by y 2 by 1 in. in 
size on the gauze. By means of a flame apply heat to the wood 
from beneath the gauze. If the flame from the burner passes 
through the gauze, more thicknesses of the gauze must be used. 
While the wood is smoking strongly, remove the flame and apply 
a lighted match to the escaping smoke. Does the smoke catch on 
fire? 'Fig. 63.) How high above the wood can you cause the 
smoke to ignite? 



BURNING OF WOOD AND COAL 83 

This smoke consists of volatile matter produced by the action 
of the heat on the wood. The volatile matter consists in part of 
hydrocarbons, and in part of water, acids, and wood alcohol. It is 
the burning of the volatile matter which causes the flame when 
wood is burned. 

The black material, left on the gauze after the volatile matter is 
removed, is called wood charcoal. Place it on the edge of the 
gauze so that the end of the stick of charcoal extends beyond the 
gauze and heat the charcoal strongly by means of a flame. Does 
the charcoal get red hot? Does it burn after the flame is removed? 
Does the charcoal burn with a flame? Does it give off much 
heat? Do you find any ash remaining after the charcoal has 
burned? The glowing embers of a wood fire are due to the burning 
of the wood charcoal after the volatile matter has been removed 
and burned. 

Caution. — Be sure to quench the glowing charcoal lying on the 
gauze by throwing it into water. Why? (c Ex. 26.) 

Exercise 30. — The Distillation of Wood 

Select a piece of wood about 1 in. long and of such a size as will 
slip into a test tube. Close the test tube with a one-hole stopper 
through which passes a short glass tube (Fig. 64). Heat the test 
tube as shown in the figure, carefully observing what takes place. 
Does smoke appear? Try lighting it as it comes from the small 
tube. Does liquid appear in the tube? Keep the tube inclined 
so that the liquid will stay near the stopper. If you allow it to 
run back and meet the hot glass it will probably break the tube. 
When the wood ceases to give off smoke, cool the tube, remove the 
stopper and pour the liquid into a shallow vessel. What is its 
color, odor, and appearance? 

84. Discussion of the Exercise. — The liquid distilled from 
the wood is known as pyroligneous (pf'ro-llg'iie-iis) acid 
(pyro meaning fire, and ligneous meaning woody). It is 
therefore, acid obtained from woody substances by means of 
fire. It is composed largely of water but it also contains 
acetic acid (the acid of vinegar) and wood alcohol and other 
substances of commercial value. When wood is burned in a 
stove or grate these substances, except the water, together 
with the gases which escaped from the tube are all consumed 
in the flames, while the charcoal remains on the grate to be 



84 THE PRODUCTION AND USE OF HEAT 

slowly oxidized to carbon dioxid, producing much heat but 
little or no flame. 

85. A Study of Flame. — It has been seen that it is the 
vapor of the candle, of the gasoline, and of the kerosene that 
burns. The hydrogen has been seen to burn with a flame. 
The illuminating gas burns w^th a flame. The volatile matter 
from the wood burns with a flame. In every case a flame is 
produced by a burning vapor, or gas. Those fuels that are 
gases or that may be changed into vapors, or gases, by means 
of heat burn with a flame. Four conditions are necessary in 
order that a flame be produced : (1) The material must be in 
the form of a vapor or gas; (2) this vapor or gas must be 
mixed with oxygen; (3) the mixture of oxygen and vapor 
or gas must have concentration within certain limits (Art. 77) ; 
(4) the mixture must be heated to the kindling temperature. 
If one or more of these conditions are wanting there can be 
no flame. 

86. Blowing Out a Flame. — A common expression is that 
of "blowing out" a flame. Candle flames, lamp flames, and 
even the flame of a fire just started may be blown out. 
However, if the fire is well started, it may be impossible to 
blow it out, but rather the blowing only serves to make the 
fire burn faster. From what has been given in Art. 85, on 
flames, it is evident that the effect of blowing into a candle 
flame or a lamp flame is to scatter the particles of vapor or 
gas and thus reduce their concentration (Art. 77) to such an 
extent that there can be no flame. Moreover, the cold blast 
of air entering the flame serves to cool the burning materials 
below their kindling temperature (Art 77). With a solid 
fuel such as charcoal, however, the case is different. 

Exercise 31. — Effect of Blowing upon Glowing Charcoal 

Place a piece of charcoal upon the gauze and heat it with a flame 
until it glows. Now blow gently upon the glowing portion. D©es 
the blowing cause it to burn more or less rapidly? Can you blow 
it out? Caution. — Quench the charcoal in water when through 
with it. 



BURNING OF WOOD AND COAL 85 

It is evident that one can not blow hard enough on the 
charcoal to scatter the particles as the gas particles are 
scattered and thus stop the burning. Rather, the blowing 
serves to bring in fresh oxygen and to remove the carbon 
dioxid resulting from the burning thus favoring the burning. 

87. Luminous and Non-luminous Flames. — In will be re- 
called that the flames of the candle, of the kerosene lamp, 
and of the burning wood are yellow or red in color and give 
much light. Such flames are said to be luminous. The 
hydrogen flame, the gasoline flame as commonly used in stoves, 
and the illuminating gas flame as used in stoves or within 
Welsbach mantles are blue. Such flames are said to be non- 
luminous. The heat of the flame causes the mantle of a gas 
lamp to become very hot and thus to give light. The light 
producing ability of the flames of the candle, or kerosene, 
and of wood is due to the presence of red- or white-hot parti- 
cles of carbon. The carbon has been separated from the fuel 
burned by the action of the heat on certain compounds in the 
fuel. This carbon is heated by the burning of the hydrogen 
in the fuel and thus gives light. The carbon finally meets 
oxygen and it too burns liberating heat. If anything inter- 
feres with the burning of the carbon, a black smoke composed 
of unburned carbon particles results (Ex. 4). 

88. Incomplete Combustion. — 

Exercise 32. — Causing a Flame to Smoke 

Light a candle flame. Can you see any unburned carbon escaping 
from the flame? Now introduce some cold object, as a glass tum- 
bler, into the flame. "What is the result? What do you find is 
being deposited upon the cold surface? Why did it not burn? 

Light a kerosene lamp and replace the chimney. Turn the wick 
higher until the lamp smokes. What is the smoke? Why does 
not this smoke burn? Why does not the flame smoke when the 
wick is turned lower as it should be (Art. 8, Ex. 4) ? 

Discussion of Exercise 32. — The fuels burned in the 
above exercise were hydrocarbons. We have just seen that 




86 THE PRODUCTION AND USE OF HEAT 

the fuel suffers decomposition or a breakdown into its ele- 
ments, hydrogen and carbon, as it burns. These elements 
then burn separately. If there is a lack of suf- 
ficient oxygen, or if the fuel and oxygen 
are not properly mixed, or if the carbon is 
cooled below its kindling temperature before it 
has a chance to meet oxygen, then there will be 
more or less unburned carbon and the flame 
will smoke, due to the escape of this unburned 
Buj-nin ^th carbon - Now it happens that the volatile mat- 
volatile por- ter from wood contains some oxygen in addition 
tion of coal in to what may mix with it from the air, and con- 

air. 

sequently wood ordinarily burns without black 
smoke. It is therefore said to be a cleaner fuel than soft coal 
which ordinarily burns with a black smoke. 

89. Burning Coal. — Soft or bituminous coal is the name 
applied to most of the coal mined in the United States, except 
that which is mined in the eastern half of Pennsylvania. To 
this latter the name hard or anthracite coal is applied. 

Exercise 33. — How Soft Coal Burns 

Place two or three thicknesses of wire gauze on a ring attached 
to a ring stand and lay a piece of soft coal about the size of a 
marble on the gauze. Heat the lump strongly by means of a 
flame. Does the coal produce any smoke? Remove the flame 
(Fig. 65). Can this smoke be ignited? How far above the coal 
are you able to ignite the smoke? The smoke, or volatile matter, 
consists of water and various hydrocarbons arising from changes 
in the coal, due to the heating. After all of the volatile matter 
of the coal has been driven off, remove the flame and examine the 
part which remains. It is called coke. What is the name of the 
corresponding material obtained by heating wood? See if you can 
ignite the coke as the charcoal from wood was ignited. Coke is 
much used as fuel, especially in obtaining metals from their ores. 

Exercise 34. — How Hard Coal Burns 

Repeat the preceding experiment using a lump of hard coal in- 
stead of the soft coal. Can you heat it hot enough to drive off 



BURNING OF WOOD AND COAL 87 

enough volatile matter to support a flame? What can you say 
about the relative amounts of volatile matter in the two kinds of 
coal? 

Exercise 35. — Distillation of Soft Coal 

Arrange to distill soft coal just as wood was distilled (Ex. 30) 
except that the test tube is filled about one-thirds full of fine soft 
coal. The liquid which collects in the test tube is called coal tar, 
the gas which burned is the coal gas, while the solid portion left 
from the coal is the coke. 

90. Familiar Facts about the Burning of Wood and Coal. 

— Wood and soft coal burn with long red flames because they 
contain so much volatile matter, while hard coal, because it 
contains so little volatile matter, does not produce such flames. 
Wood and hard coal make but little smoke because they are 
completely burned, including whatever volatile matter they 
contain, while soft coal, because it contains so much volatile 
matter, produces more or less black smoke. Hard coal and 
wood produce light fleecy ashes, while those from soft coal 
often melt together in the fire, causing clinkers. For starting 
a wood or a soft coal fire, a rather small amount of kindling is 
needed, since these fuels catch on fire easily because of their 
large amounts of volatile matter which easily ignites. Hard 
coal, because it contains so little volatle matter, requires more 
kindling and a hotter fire to start it. 

91. The Composition of Common Solid Fuels. — In our 
study of fuels it is important that we understand the be- 
havior of the fuel when heated. The following table gives: 
(1) The percentage of carbon that does not pass away as 
volatile matter, known as charcoal, coke or fixed carbon; (2) 
the percentages of volatile matter which is produced by the 
fuel when it is heated; (3) the percentage of water; (4) the 
percentage of ash. 

In the construction of stoves and furnaces in which the 
various fuels are to be burned, the manufacturer must keep 
in mind these facts of composition. The customer who buys 
a stove or furnace must know in general what kind of fuel is 



88 



THE PRODUCTION AND USE OF HEAT 



to be burned. Even with all of these conditions in mind, it 
is yet a difficult matter to burn soft coal, which produces 
much volatile matter, in such a way as to avoid serious loss. 

Table II. — Composition of Solid Fuels 







Coke or 


Volatile 


Moisture, 


Ash. 




Substance. 


fixed carbon, 
per cent. 


matter, 
per cent. 


per cent. 


per cent. 


Wood 


dried 


20 to 30 


55 to 65 


15 to 20 


l»to 3 


Peat, 


dried ■ 


25 to 35 


25 to 50 


20 to 35 


2 to 7 




Lignite 


40 to 70 


23 to 48 


4 to 40 


3 to 20 




Cannel 


30 to 40 


45 to 55 


lto 4 


6- to 12 


Coal 


Bituminous .... 


40 to 75 


20 to 50 


3 to 10 


2 to 10 




Semi-bituminous 


70 to 80 


10 to 20 


lto 5 


4 to 10 




Semi-anthracite 


80 to 90 


5 to 10 


lto 3 


3 to 7 




Anthracite 


85 to 93 


3 to 6 


lto 3 


3 to 5 


Coke 




85 to 95 


none 


lto 5 


2 to 12 



IV. SMOKE; ITS CAUSE AND PREVENTION 

92. The Cause of Smoke. — Because of the high percentage 
of volatile matter in soft coal, it is likely to produce much 
black smoke unless precautions are used to prevent it. The 
principles concerned in smoke production are identical with 
those explained in connection with the smoking candle and 
the oil lamp. Hydrocarbons produced by the heated coal are 
decomposed more or less completely into hydrogen and car- 
bon. Failure of the carbon to meet a sufficient supply of 
oxygen at or above the kindling temperature of the carbon, 
causes more or less of the carbon to be carried up the chim- 
ney unburned, making its appearance as black smoke. Even 
though the temperature of volatile matter is kept sufficiently 
high until it meets oxygen, if the supply of the latter is 
insufficient, the carbon will be incompletely burned at best. 
It may be burned to carbon monoxid instead of carbon 
dioxid. This means a loss of heat, since less than one-third 
of the energy of the carbon is liberated as heat if it is burned 
to carbon monoxid instead of carbon dioxid. 



SMOKE; ITS CAUSE AND PREVENTION 89 

93. Some of the Evils of Smoke. The Smoke Nuisance. — 
The production of black smoke means, not only poor com- 
bustion of the coal and hence a loss of heat, but also injury to 
health and property. People who are compelled to live and 
work in a smoky atmosphere are liable to injury to their 
health. Moreover, the smoke and its accompanying dirt have 
a depressing effect on people. They are liable to become de- 
spondent and unhappy. This in turn may affect their health. 
Smoke makes necessary the more frequent painting of build- 
ings. Stone buildings become dingy and the owners are 
sometimes put to the expense of washing the entire outside 
of the building. White clothing becomes soiled because of 
soot. Furnishings and draperies in houses are injured. 
Goods on the dealer's shelves are injured because of soot. 
Our waste due to poor combustion of soft coal runs into 
millions of dollars annually. 

94. How Can This Waste be Prevented? — Of course, the 
prevention is by causing more perfect combustion of soft 
coal. Did you ever follow the changes that take place when 
fresh, soft coal is thrown into a stove containing a bed of hot 
coals? When the coal first meets the hot bed of coals the 
volatile matter of the coal begins to distill off. If the tem- 
perature in the stove is fairly high, this volatile matter may 
undergo more or less complete decomposition into carbon 
and hydrogen. The hydrogen burns if the oxygen supply 
is somewhat limited, while the carbon, which requires a 
greater concentration of oxygen, is burned incompletely or 
not at all. Black smoke results. If the temperature in the 
stove is rather low, the volatile matter may not be decom- 
posed so much. A bluish-gray smoke results. At all events 
the drafts of the stove are generally not able to supply enough 
oxygen and maintain at the same time a temperature high 
enough to burn the volatile matter immediately after throwing 
fresh coal into the fire. Consequently smoke issues from the 
chimney as long as there is much volatile matter being pro- 
duced from the coal. After the volatile matter has been 



90 



THE PRODUCTION AND USE OF HEAT 



set free, smoke ceases to escape from the chimney until a 
fresh charge of coal is thrown into the stove. If smaller 
amounts of coal could be thrown in at shorter intervals of 
time, it might be that the drafts of the stove would be able to 
supply enough oxygen to burn the volatile matter as fast as 
it is produced by the coal. Since it is not convenient to place 
frequent small charges of coal in the stove, the other method 
commonly resorted to in smokeless combustion is the gradual 
and slow distillation of the volatile matter in the soft coal, so 
that the drafts can furnish oxygen fast enough to consume the 
volatile matter completely. 




J^^> 



1 ig. 66. — Stove with air blast. 




Fig. 67. — Another form of air blast. 



95. How Some Stoves and Furnaces are Constructed to 
Prevent Smoke. — A common device is the hot blast stove. 
In this stove the air for the oxygen supply is admitted from 
above instead of from beneath the grate as in most stoves. 
By the top-draft arrangement, the volatile matter has a better 
chance to meet oxygen and hence its complete combustion 
is more -readily accomplished (Figs. 66 and 67). 

In some furnaces the coal is first thrown into a coking 
chamber which is heated by the fire in the fire pot. Here slow 



SMOKE; ITS CAUSE AND PREVENTION 



91 




Fig. 68. — A furnace with a coking chamber. 




Fig. 69 — Coking chamber of a 
side-feed furnace. 




Fig. 



underfeed furnace. 



92 



THE PRODUCTION AND USE OF liEA^T 



distillation of the volatile matter takes place. By means of 
a damper in the coking chamber door, sufficient air can be 
admitted and a sufficiently high temperature may be main- 
tained in the combustion chamber to burn the volatile matter 
completely (Figs. 68 and 69). 




Fig. 71. — Showing the feed cylinder tilted forward and filled with 
coal. The apron closes the opening in the center of the grate through 
which the coal is forced upward into the fire box. 

In the underfeed furnace, fresh coal is introduced at the 
bottom of the fire bed. Distillation of the volatile matter 
takes place therefore at the bottom of the fire, where the 
oxygen supply may be more abundant than on top of the 




Fig. 72. 



-Showing the fresh coal forced into the fire box and the burning 
coal resting on the top of the fresh coal. 



fire, and hence it is more completely burned (Figs. 70, 71, 
and 72). Moreover, in passing through the glowing coke 
above, the volatile matter is sure to be heated to the kindling 
temperature. 



LIQUID FUELS 



93 



In steam boiler plants mechanical stokers are often em- 
ployed. With the mechanical stokers, the aim is to feed the 
fuel to the lire gradually by some device. In the stoker 
shown (Fig. 73), which is a chain grate stoker, the coal is fed 
continually by being carried into the furnace on the grate. 
As the fresh coal approaches the zone of combustion, the 
volatile matter is gradually distilled from the coal. There is 
also provision for a supply of air ample to burn the volatile 
matter as well as the fixed carbon or coke. 




Fig. 73. — Mechanical stoker and a water-tube boiler. B, Chain grate. 
C, Fresh air. G, H, Baffle plates. iY, Water feed pipe. R, Blow off. 
S, Steam dome. Y, Pressure gage. X, Safety valve. 



V. LIQUID FUELS 

96. The Burning of Liquid Fuels. — The burning of kero- 
sene and of gasoline has already been studied. It will be 
remembered that, in each case, the liquid is first converted 
into a vapor, and then the vapor is burned, using an adequate 
supply of air. The same principle is used in burning liquid 



94 



THE PRODUCTION AND USE OF HEAT 



fuels generally. Crude petroleum is burned by vaporizing 
it by means of a jet of air or steam, after which the vapors 
are burned in the proper supply of air. The gasoline in the 
automobile is vaporized and mixed with the proper amount 
of air in the carbureter, after which the mixture is drawn 
into the cylinder, compressed to increase the rate of com- 
bustion, and finally burned within the cylinder (see Gas 
Engines, Chap. XI). 

VI. GASEOUS FUELS 

97. Gaseous Fuels. — These have long been a favorite kind 
of fuel. Their use in the home and in various industries 




TTT^TTPTTT^ 



c/ryj^x/sv 



Fig. 74. — An illuminating coal gas plant. 



has gradually increased. Gaseous fuels are commonly trans- 
mitted from producer to consumer in pipes. The cost of 
pipes makes it unprofitable to transmit the fuel long distances. 
Some gases, as acetylene, are transmitted under pressure in 
metal tanks. The material for making acetylene, calcium 
carbide, may be transmitted long distances profitably. 

98. Coal Gas. — Coal gas was the first manufactured gas. 



GASEOUS FUELS 



95 



It was used for lighting the streets of London and Paris more 
than 100 years ago. In 1817, the city of Baltimore began 
to use it for street lighting. The gas is made by distilling 
soft coal in air-tight retorts (Fig. 74). The coal contains 
many hydrocarbons which leave it when the coal is heated. 
The hydrocarbons at the same time are broken down into 
simpler compounds. The gas also contains hydrogen and 
carbon monoxid. Because of the hydrocarbons in coal gas it 
burns with a luminous flame. The manufacture of coal gas 




GENERATOR CARBURETER SUPERHEATER 

Fig. 75. — Water-gas apparatus. 



has gradually declined of late owing partly to the fact that 
but few kinds of coal are suitable for use in making it and 
these are becoming more expensive, and partly to the decrease 
in the cost of electricity. 

99. Water-Gas. — "Water-gas has come to replace coal gas 
in many cities. When steam is passed over red-hot carbon, 
the former is decomposed into hydrogen and oxygen. The 
carbon then unites with the oxygen from the steam to form 
carbon monoxid or carbon dioxid depending upon conditions, 



96 THE PRODUCTION AND USE OF HEAT 

while the hydrogen from the water is set free. By proper 
control of conditions, carbon monoxid rather than carbon 
dioxid may be formed, which, with the hydrogen set free, 
makes a mixture of highly combustible gases. The mixture is 
called water-gas. During the chemical reaction of the steam 
and the hot carbon, heat is absorbed, and consequently the 
carbon soon cools to a temperature at which the reaction 
stops. The carbon is then heated again by blowing air through 
the furnace, called the generator (Fig. 75), in which it is 
contained. When the carbon again becomes hot enough, the 
air is shut off and steam is again admitted. Since the carbon 
monoxid and the hydrogen burn with a blue flame, it be- 
comes necessary to introduce some substance that will render 
the flame of water-gas luminous. This is done by introducing 
into the gas vaporized, or gasified, hydrocarbons derived from 
crude petroleum. The petroleum is sprayed into a carbur- 
eter which is heated to a very high temperature. Here the 
\etroleum hydrocarbons are broken down into simple hydro- 
carbons which remain as gases. These are mixed with the 
water-gas and the mixture is passed through the superheater. 
Such a mixture is known as carburetted water-gas. 

ioo. Gasoline Gas. — Gasoline gas is simply air and gasoline 
vapor mixed in such proportions as to be non-explosive. Air 
containing less than 1.5 per cent, and more than 6.4 per cent, 
of gasoline vapor, by volume, when 88°B. gasoline is used, is 
non-explosive, while a mixture containing between 1.5 per cent, 
and 6.4 per cent, of gasoline is explosive. There are two gen- 
eral processes used for vaporizing the gasoline. One, known 
as the cold process, is described in Art. 39. For this, a light 
oil (88°B.) must be used. The other process, known as the 
hot process, uses heat to vaporize the gasoline. This makes 
possible the use of a heavier, and hence a cheaper, grade of 
gasoline. In each of these systems, it is expected that the 
air will carry from 12 to 20 per cent, of gasoline vapor. 
Gasoline gas is almost always used with a mantle when used 
to produce light. It may be used in ranges for cooking. The 



THE MEASUREMENT OF HEAT 



97 



production of gasoline gas offers a convenient means of pro- 
ducing gas in small amounts for home or school use in places 
inaccessible to a city gas supply. 

Table III. — Composition of Gaseous Fuels (Approximate) 





Combustible constituents 


Non-combustible 
constituents 


B.t.us. 
per cubic 


Kind of gas 


Hydro- 
gen 
. per cent. 


Hydro- 
carbons, 
per cent. 


Carbon 
monoxide, 
per cent. 


Carbon 
dioxide, 
per cent. 


Nitro- 
gen. 


foot 

(see Art. 

122) 


Natural gas 
Coal gas . . 
Water-gas . 
Gasoline gas 


0.0 
41.3 

38.0 
0.0 


99.0 
49.0 
19.0 
15.0 


0.4 

6.4 

33.0 

0.0 


0.3 
2.0 
4.0 
0.0 


0.2 
1.0 

5.0 
68.0 


900 
600 

600 

540 



VII. THE MEASURE OF HEAT 

Our fuels are burned for the production of heat or light. A 
fuel intended for the production of heat is more or less valu- 
able depending on the amount of heat that can be obtained 
from it when it is burned. 

ioi. Distinction Between Heat and Temperature. — We 
have learned that temperature refers to the hotness or cold- 
ness of a body (see Art. 14). Temperature is measured by 
means of a thermometer. Two bodies may have the same 
temperature but may contain vastly different amounts of 
heat. A pint of Avater may have the same temperature as 
the average temperature of a large body of water like Lake 
Michigan, yet it will possess very little heat compared with 
that in the lake. The lake influences the climate of the sur- 
rounding states, but the influence of the pint of water on the 
temperature of objects around it will amount to almost nothing. 
It is apparent that the weight of the body has a great deal 
to do with the heat it contains at a given time. Then, too, 
the amount of heat a body contains also depends upon the 
material of which it is made. Two objects of the same weight 
but of different materials may be changed in temperature an 



98 THE PRODUCTION AND USE OF HEAT 

equal number of degrees, and yet the amounts of heat required 
to produce the change in temperature may differ greatly. 
One pound of water in being raised in temperature 10° C. 
will require more than 32 times as much heat as will be 
required by 1 pound of lead raised a like amount in tempera- 
ture. Other substances require still different amounts of heat 
for a like temperature change. 

Definition. — The heat capacity of 1 gram of a substance 
while being raised 1°C. is called the specific heat of that 
substance. 

So it is evident that the heat an object possesses depends 
upon three factors: (1) Its weight; (2) its temperature; (3) 
the material or substance of which it is composed. 

102. Units of Heat Quantity. — ' 

Definitions. — 1. One unit is the amount of heat necessary 
to raise 1 gram of water 1° C. It is called the lesser calorie 
and this is usually abbreviated thus: 1 cal. 

2. A second heat unit is the amount of heat necessary to 
raise 1000 grams, ,or 1 Kg., of water 1°C. It is called the 
greater calorie and is usually abbreviated thus: 1 Cal. This 
is the unit generally used by European engineers in calculating 
all large quantities of heat, such as are required in heating 
buildings. 

3. A third unit is the amount of heat required to raise the 
temperature of lib. of water 1°F. This is called the British 
thermal unit. In writing it is usually abbreviated, thus: 
1 B.t.u. This is the unit commonly used by British and 
American engineers. 

Table IV. — Heat Value of Fuels (Approximate) 

> Calories per pound B.t.us. per pound 

Carbon 3,672 14,544 

Hydrogen 15,664 62,032 

Wood, Ash 2,141 8,480 

Wood, Beech 2,161 8,591 

Wood, Oak 2,100 8,316 



OUR COAL SUPPLY 99 



Wood, Pine 2,311 9,153 

Wood, Elm 2,150 8,510 

Charcoal 3,227 12,780 

Peat 1,800 to 2,300 7,200 to 9,000 

Lignite 1,800 to 3,000 7,200 to 11,700 

Coal, Bituminous 3,000 to 3,600 11,700 to 14,400 

Coal, Semi-anthracite 3,000 to 3,600 11,700 to 14,400 

Coal, Anthracite 3,400 to 3,900 13,500 to 15,300 

Coke 3,450 to 3,7*00 13,700 to 14,500 

Petroleum about 5,000 about 20,000 



VIII. OUR COAL SUPPLY 

103. Development of Coal Production. — The first coal pro- 
duced in the United States was mined and marketed in 1820. 
The records show that 365 tons, an average of 1 ton per day, 
were produced that year. For many years the production 
of coal increased slowly. During past years the increase 
in production of coal has been very rapid, till in 1918 about 
580,000,000 tons were mined and used. The diagram, Fig. 
76, shows that until 1907 the production of coal in the 
United States has doubled about every ten years. If this 
rate of increase in the use of coal were to continue in the 
future, we should consume in 1920 about 1,000,000,000 tons; 
in 1930 about 2,000,000,000 tons . in 1940 about 4,000,000,000 
tons, and so on. At this rate of increase, how many tons will 
we require in the year 2000? How many tons in the year 
2040 ? Is it probable that this rate of increase will continue ? 

104. Waste in Mining of Coal. — In mining coal, it has gen- 
erally been found necessary to leave large columns of coal to 
support the roof of the mine. In the anthracite fields of 
Pennsylvania more than one-half of the coal is thus left in the 
mine — only about 40 per cent, is removed. The remaining 
60 per cent, of the coal is left in such shape that it can 
probably never be recovered. This means that for every ton 
of anthracite coal which has been mined about 1% tons have 
been forever lost to the use of mankind. In the bituminous 



100 



THE PRODUCTION AND USE OF HEAT 



fields, there has been less waste. For every ton of bituminous 
coal mined about % ton has been left in the mine. 

105. How Long Will Our Coal Supply Last? — Govern- 
ment officials have made careful estimates of the number of 
tons of coal in all known coal deposits of the United States. 
Accepting this estimate and supposing that the consumption 
of coal will continue to increase at the same rate in the future 
as it has in the past, it has been shown that our available 





Tons 






:::::::::::::::::::::::::::::::::::::::::: :::::/::: 


r 






:::: :::::::::::::::::::::::::::::::: :::: 1:2. : : 










■i> 




300,000,000 ::::::::::::::::::::::::::::::::::::::::]::::::: : : 


/ 


z 




~.& r 


JL 


ft 


/*J 




__*< 


7 


-" 


1820 
1830 
1840 
1850 
1860 
1870 
1880 
1890 
1900 
1910 
1920 



Fig. 76. — Annual production of coal in the United States, 1820 — 1920. 



coal supply will be exhausted in about 120 years, or about the 
year 2030. We therefore see how necessary it is that we 
avoid as far as possible all waste of coal. 

At the present time a much larger portion of our coal is 
being wasted than is being used for the benefit of mankind. 
The two chief sources of loss are : 

1. Only about one-half of the coal is being removed from 
the mine ; the other half is being left in such a condition that 
it probably can never be recovered. 



OUR COAL SUPPLY 



101 



2. We have seen in the preceding pages of this chapter, 
that only a small portion of the energy in the coal bnrned is 
now being utilized. 

106. The Coal Fields of the United States.— The map, 
Fig. 77, shows the location of the more important coal fields 
of the United States. The large eastern field extending from 
Pennsylvania to Alabama yields chiefly anthracite, semi- 
anthracite and semi-bituminous coals. The central fields, 
consisting of the Illinois, Indiana, Kentucky, Iowa, and Mis- 
souri fields yield chiefly bituminous and cannel coals. The 




Fig. 77. — Distribution of coal fields in the United States. 

large northwestern field of the Dakotas, Montana, and Wyom- 
ing yields bituminous and lignite coals. The fields of Col- 
orado yield bituminous and semi-anthracite coals (see Table 
II, Art. 91, Composition of Solid Fuels, for the distinction 
in different kinds of coals). 

IX. DEVELOPMENT OF HOUSE HEATING 
107. The Roman Hypocaust. — The houses of the Romans 
were heated by hypocausts. These were fire rooms con- 



102 



THE PRODUCTION AND USE OF HEAT 



structed in the cellars (Fig. 78). From these rooms clay 
pipes led to various rooms of the house above. Through these 
pipes all of the smoke and heat from the burning wood passed 
to the rooms above. This method of heating would seem 
very disagreeable to us, especially when the volatile matter 
was distilling from the wood. Crude as this method of 
heating was, it was the best method known until compara- 
tively recent times. The use of the hypocaust perished with 
the civilization of Rome. 




Fig. 78. — A Roman hypocaust. (From Stories of Useful Inventions. 
By permission of The Century Company.) 

108. The Fireplace and the Early Stoves. — Mention has 
already been made of the use of the fireplace in house heating 
and cooking, and of Franklin's invention of the stove. Stoves 
did not come into general use in the United States until after 
1825. Wood was used as the fuel and the stoves were but 
little more than open, iron fireplaces standing out in the 
room. Between 1825 and 1835, the first stoves for burning 
hard coal were made. Some of these were fairly successful 
but all have been greatly improved since that time. 



DEVELOPMENT OF HOUSE HEATING 103 

109. The Invention of the Chimney. — It is recorded that 
the invention of the chimney was the result of war. At the 
time of the Norman conquest of England in 1066 the Britons 
heated their houses by means of fires built on the floor at 
the center of the house. The smoke was permitted to escape 
through a hole in the center of the roof. But the smoke so 
bothered the Britons as they fought from the house roofs that 
the custom arose of building a fire at one side of the room 
and providing for the escape of the smoke through an opening 
in the side wall. To cause the smoke to escape more readily 
through the opening, a hood was built into the room over the 
fire. From this crude beginning chimneys finally developed. 

Causes of Convection Currents 
no. Some Common Observations. — You have very likely 
noticed many times that when a fire in the stove is first 
lighted the draft is not strong for a minute or so. As soon 
as the fire is really burning well, the draft becomes strong. 
When we first light a bonfire, the feeble flame is blown about 
in all directions by the breezes. When the fire gets to burning 
fiercely, all these conditions change. Instead of being carried 
off by the wind, the smoke and burning embers are swept 
swiftly upward, rising in a vertical, tapering column to the 
height of 20, 30 or perhaps, 50 ft. If we notice carefully now, 
we shall see that the wind blows into the fire at the ground 
from every direction. The rising column of air is called a 
convection current. We shall be able to understand this 
better if we learn what effect the heating of air has upon its 
volume. 

in. Effect of Heat upon the Volume of Air. — 

Exercise 36. — Air Expanded by Heat 
Fit a 10- or 12-in. glass tube into the stopper and the stopper into 
the flask. Be sure that the apparatus is air-tight (Fig. 79). Invert 
the flask so that the end of the tube dips into the water in a vessel. 
Gently apply heat to the flask, constantly turning it so as to heat it 
evenly on all sides. Do bubbles of air escape from the tube? Heat 
the flask quite hot ; then remove the flame and allow the flask to cool. 




104 THE PRODUCTION AND USE OF HEAT 

What happens? What portion of the air was forced out of the 

flask? 

When air is heated, it always expands. When a certain 
volume of air at the temperature of freezing water is heated 
to the temperature of boiling water, it increases nearly % in 
volume. If it is heated but 1°C, it in- 
creases exactly % 73 part of itself. This 
fact was discovered by a Frenchman 
named Charles in 1787. He discovered 
that this was the rate at which all gases 
expand when heated. This fact is 
called Charles' law and is stated thus: 
Pressure remaining constant the volume 
of a giv'en portion of gas increases % 73 
part of its volume at zero centigrade for 
Fig. 79.— Effect of heal 6ac ft r j se f y>Q t ahove that temperature, 
upon volume of air. . , 7 . ; J 

and it decreas-es' >273 of its volume for 
each fall of 1° below that temperature. 

ii2. Application of Charles' Law. — It is not probable that 
in any two lamps we might examine we should find that the 
gases within the chimney are heated to exactly the same 
temperature. But we are probably not far from the truth 
if we say that the gases within the ordinary lamp chimney 
are so heated that they are expanded to twice the volume they 
had when they entered the bottom of the burner. Every 
cubic inch of air which enters the burner leaves the top of 
the chimney as 2 cu. in., if this be true. The same thing takes 
place in the bonfire. As soon as the fresh air reaches the 
heated portion of the fire it is greatly expanded. The coal 
in the stove or furnace produces a still higher temperature. 
The air passing up through the bed of glowing coke is so 
heated at that moment that it is increased to three or possibly 
five times its volume as it enters the damper. It is this heat- 
ing of the air and the consequent expansion, or increase in 
volume, which produces convection currents. Just why and 
how this is so we must learn. 



DEVELOPMENT OF HOUSE HEATING 105 

113. Floating Bodies and Buoyancy. — We all know that a 
cork or a piece of wood weighs less than a piece of iron of 
the same size. We also know, that if we place the cork or 
piece of wood in water, it will float, while if we place the 
iron in water, it sinks. What makes the cork float? Just 
why does the iron sink? Does the iron have any tendency to 
float ? Answers to these questions will help us to understand 

CONVECTION CURRENTS. 

Exercise 37. — Floating Bodies and Buoyancy 

(a) Place a cork in a basin of water. Does it float entirely upon 
the surface? If any portion of the cork is below the surface of 
the water, about how much of it is so? Does 
"floating upon the water" mean that all of 
the body is above the level of the water? 
Does the cork have any tendency to sink? 

(&) Set a small pail in an empty basin. 
See that the pail is exactly level. Fill it 
exactly full of water. Take care that no 
water runs over into the basin. Now tie a 
cord securely around a stone. Weigh the 
stone by means of a spring balance. While Fig. 80. — Buoyancy, 
the stone is still suspended from the balance, 

lower it into the pail of water till it is entirely covered by water. 
At the same time the stone must not touch the bottom of the pail. 
See how much the stone now seems to weigh (Fig. 80). How 
much has it lost in weight? 

(c) Carefully remove the stone from the water. Remove the pail 
from the basin. You now have in the basin the water which ran 
over when the stone was immersed in the pail. Empty the water 
out of the pail and pour the water from the basin into it. Weigh 
the pail and this water. Now empty out this water and weigh the 
pail. The difference in these last two weights gives you the weight 
of the water which ran over when the stone was immersed in the 
water. The difference between the two weights of the stone gives 
the loss of weight which the stone seemed to suffer upon being 
immersed. How does this loss of weight compare with the weight 
of the water which ran over? What is now your answer to the 
question: Does the stone have any tendency to float when im- 
mersed in water? To what extent does the water lift or hold up 
the stone? Repeat the experiment. 

(d) Fill the pail partly full of water again. Now hold the cork 




106 THE PRODUCTION AND USE OF HEAT 

down near the bottom of the water and release it. What happens? 
To what extent does the water lift, or force up, the cork? If you 
had a body exactly as dense as water, i.e., which weighs exactly the 
same per cubic inch, would it float or sink? What would it do? 

114. Archimedes' Principle. — In performing part (c) of 
the preceding experiment, a student got the following results : 

Weight of the stone in air 46 oz. 

Apparent weight of the stone immersed in water. . . 30 oz. 

From which we get the loss in weight 16 oz. 

Weight of pail and water which ran over 23 oz. 

Weight of the pail empty 7 oz. 

From which we find the weight of water 16 oz. 

From this experiment the student concluded that the loss 
of weight by the stone when immersed in water was equal to 
the weight of the water displaced. 

This truth was first stated by a Greek philosopher named 
Archimedes who lived about 25 years before Christ in an- 
cient Syracuse. He was a close friend of King Hiero; his 
life was spent in the study of mathematics and science. He 
w T as the most profound student of these subjects in his day. 
It is said that his friend, King Hiero, ordered from his gold- 
smith a crown of pure gold. When the crown was completed, 
how r ever, the king suspected that it was not pure gold. He 
summoned Archimedes and instructed him to ascertain the 
truth without injuring the crowm. Archimedes was pondering 
over this question as he went to his daily bath. Noticing, as 
he entered the full bath, that the water was lifted and ran 
over the edge of the tub just in proportion as his body was 
immersed, and also that his own weight was decreased at the 
same time, he leaped from the bath and ran to his home 
shouting, " Eureka, Eureka," which means "I have found it, 
I have found it." Pure gold is a little more than nineteen 
times as heavy as water, where silver is but ten and one-half 
times as heavy. If the crown had been pure gold it should 
have lost one-nineteenth of its weight when immersed in 



DEVELOPMENT OF HOUSE HEATING 107 

water. He found that it lost more than one-nineteenth of its 
weight, so he concluded that silver had been used in its con- 
struction. 

Archimedes' principle may be thus stated: Whenever a 
body is immersed in a fluid (liquid or gas) it is buoyed up with 
a force which exactly equals the weight of the fluid displaced. 

When the cork was immersed in the water (d, Ex. 37), it 
was being pushed upward with a force equal to the weight of 
an equal volume of water. Since the weight of the cork was 
less than this force, it was pushed to the surface of the water 
and partly out of it. As it floated upon the surface of the 
water, it was displacing an amount of water which exactly 
equaled it in weight. The stone, on the other hand, sank to 
the bottom because it was heavier than an equal volume of 
water ; its weight was therefore greater than the buoyancy of 
the water. That it was buoyed up to a considerable extent, 
was shown by the balance. 

115. Convection Currents Caused by the Buoyant Effects 
of the Air. — The solid portion of the earth is covered by an 
ocean of air many miles, probably some hundreds of miles, in 
depth. This air has weight, just as water has weight. In 
fact, it is much heavier than we usually suspect until we have 
weighed some of it. A box 2 ft. by 2 ft. by 3 ft., or 12 cu. ft., 
holds 1 lb. of air. A common schoolroom 30 ft. by 30 ft. by 
10 ft. therefore holds 750 lbs. of air. 

All bodies here on the earth's surface are being buoyed up 
by this air exactly as the stone and the cork were buoyed 
up by the water. A stone will fall through the air and rest at 
the bottom of the atmosphere exactly as it fell through the 
water and rested at the bottom of the pail. Even the cork 
is so much heavier than the air that it, too, sinks to the bottom 
of the atmosphere. There are some substances lighter than 
the air. Hydrogen weighs but about one-fifteenth as much 
as the air. A balloon is a bag filled with this very light 
hydrogen or some other light gas. Whenever the bag and the 
hydrogen which it contains weighs less than the air it displaces, 




108 THE PRODUCTION AND USE OF HEAT 

the surrounding air buoys it up with a force greater than 
its weight and it floats. Instead of using hydrogen, heated 
air is often used in toy balloons. The toy Fourth 
of July balloon consists merely of a sack of light, 
nearly air-tight material, usually paper. The bag 
is inverted and its lower end is somewhat open 
(Fig. 81). A burning candle is suspended in the 
Fig. 81. °P en mouth of the sack. The heat from the candle 

Hot-air keeps the air in the balloon warm. As long as this 

air is sufficiently heated, the balloon continues to 
float. The important thing to notice is this : The heated air 
would be buoyed up* pushed upward, just the same if it were 
not enclosed in a sack. From this fact we see that convection 
currents are always produced when any fluid is heated more at 
one point than at surrounding points. 

We shall find convection currents of great importance in 
the study of the weather, Chap. III. 

Application op Convection Currents to Chimneys 

i i 6. The Draft in the Chimney. — The current of air, or 
draft, in the chimney is caused by the column of air within 
the chimney becoming either warmer or cooler than the sur- 
rounding air. If the air within the chimney is warmer, the 
draft will be upward. Why? When there is a fire in the 
furnace or stove, the air within the chimney will be heated 
and the draft will be upward. It is now evident that the 
draft is not strong when we first light a fire in the stove be- 
cause the air within the chimney has not yet been heated. 

Conclusion. — There is nothing mysterious about the draft 
of a chimney. A chimney will "draw" if the laws of physics 
have been regarded in the construction of the chimney and in 
the operating of the stove. A column of heated air is lighter 
than a column of cold air and will, therefore, be pushed up 
through and out of the top of a chimney, unless there is some 
other force opposing its motion. 



DEVELOPMENT OF HOUSE HEATING 109 

Application op Convection Currents to Room Heating 

117. Convection Currents in a Room Heated by Means 
of a Stove. — Convection currents play an important part in 
all heating of rooms by means of stoves. The movements 
of air in a stove-heated room can easily be determined by 
experiment. 



Exercise 38. — Air Currents about a Stove 

Close all windows and doors. Light some punk or a piece of 
cotton elotli and test the currents of air by holding the torch in 
the following positions and observing the movement of the smoke: 
First, above the stove; on each side of the stove, level with the top 
of it; on each side of the stove and about 6 in. from the floor. 
Second, hold the torch 6 in. or 1 ft. from the ceiling and about half 
way from the stove to the window or outside wall; do this on each 
side of the room. Third, hold the torch about 3 ft. from the floor 
and about 6 in. or 1 ft. from the window or outside wall. Fourth, 
hold the torch 6 in. from the floor and half way from the outside 
walls to the stove. Show by means of a sketch the air currents as 
you found them. If some of the walls of the room are inside walls, 
the circulation will hardly be as perfect as it would be if they were 
all outside walls. 

The general circulation about the stove in a room having 
all four of its walls outside walls is very simple. There is a 
rising column about and above the stove. As this column 
pours upward against the ceiling, it spreads out in every 
direction toward the outside walls. The outside walls, and 
especially the windows, are cold, consequently the air is here 
chilled. It therefore becomes heavy and drops to the floor. 
Across the floor from every side of the room the cold stream 
of air passes back to the stove. As a person sits facing the 
stove in such a room there is sure to be a stream of cold air 
blowing against his back and past his feet. This is especially 
true if the stove is not large enough to heat all the air in 
the room. These returning currents of air are often mis- 
taken for cold, outside air which is supposed to have crept 



110 



THE PRODUCTION AND USE OF HEAT 



in through cracks and crevices about the windows and in 
the outside wall. If the walls of the room were air-tight 
these currents would still exist. 

The Setting of. Furnaces 

i i 8. The Furnace. — The Furnace for house heating is 
little more than a large stove of simple construction inclosed 
within a sheet-iron jacket or surrounded by brick walls. 




Fig. 82. — Furnace and air supply. 

When the iron jacket is used it is said to have a portable 
setting; when the brick walls are used it is said to be a 
brick set furnace. The furnace is set in the basement or 
cellar. The air to be heated is led to the bottom of the space 
inclosed by the jacket by means of sheet-iron pipes running 
through the basement, or better still, by means of large tile 
or cemented brick passages beneath the basement floor. The 



DEVELOPMENT OF HOUSE HEATING 111 

heated air is led upward from the top of the jacket to the 
rooms above, which are to be heated. 

1 19. Air Supply for the Furnace. — The cold air supplied 
to the furnace is often taken from within the house ; a more 
sanitary method is to supply the furnace with pure, fresh air 
from without the basement wall. When the second plan is 
followed, the furnace becomes, not only a heating plant, but 
also an .excellent means of furnishing ventilation as well. By 
this plan, a considerable stream of fresh air is coming into 
the house at all times. This is, of course, quite impossible 




Fig. 83. — Basement plan for setting a 
furnace. 

unless some opening is provided to allow an equal amount of 
air to escape. The ordinary house is often too well built to 
permit this amount of air to escape through cracks and 
crevices. The exit may be provided by partly opening a 
window ; it is better, however, to provide fireplaces with flues 
extending above the roof. Many people do not yet appre- 
ciate the great importance of proper ventilation for their 
homes and therefore they provide for taking the cold air 
supply only from within the house. This practice is a saving 
of fuel, for none of the air within the house is very cold at 



112 



THE PRODUCTION AND USE OF HEAT 



any time. A common practice, which can be made to meet 
the wishes of all, is so to construct the cold air duct, as it is 
called, that the air may be taken either from within the house 
or from the outside as is desired (Fig. 82). 

120. Placing the Registers and Risers. — The pipes which 
lead up from the furnace open into the rooms by means of 
registers, open frameworks of iron. The pipes leading from 




Fig 84. — First floor plan for setting a 
furnace. 



the furnace to the second floor or higher are made of tin, 
are rectangular in shape and usually about S 1 ^ in. by 12 in. 
so as to be easily placed within a 4-in. wall. These hot air 
pipes are called risers, or stacks. 

One general rule should be followed: All heating pipes 
should be as short as possible; all risers should be placed in 
inside walls; and all registers shoidd be placed as far as pos- 



DEVELOPMENT OF HOUSE HEATING 113 

sible in the warmest portion ,of the room. The reason for 
this rule is easily seen. Just as the tallest chhnney produces 
the best draft because it contains the longest column of heated 
air, so the upward current of air through the furnace, through 
the riser which leads from it and into the room above will 
be strongest if the air is well heated throughout its entire 
course. By placing the riser in inside walls and the register 
in the warmest portion of the room, which is usually also 




Fig. 85. — Second floor plan for setting a 
furnace. 

near an inside wall, a column of heated and consequently light 
air, of the greatest possible length is assured. Were the reg- 
ister placed at the coldest point in the room, the upper por- 
tion of the column would be cold air, and consequently heavy 
air, and the movement of the air through the furnace and 
the riser would be slow and sluggish. A strong and reliable 
circulation of air is the keynote to success in furnace heating. 
In Fig. 82 the circulation of air from a furnace is made 



IU 



THE PRODUCTION AND USE OF HEAT 



clear. It will be noted that floor registers are used for the 
first floor rooms and all wall registers for the second floor 
rooms. In some houses each room on the second floor is pro- 
vided with a flue for the return of cold air to the furnace, if 
inside circulation is the system to be used. These are not 
often provided, however. A good circulation is secured by 
permitting the cold air to return down the stairway (see 
plans, Figs. 83, 84 and 85). 

121. A Successful Furnace. — To be a success, the furnace 
should be so constructed and so set as to accomplish the fol- 
lowing results : 



OKSPAZOA^ P/P£ 




Fig. 86. — A hot water system. 



1. There should be a large volume of moderately heated air 
passing through the furnace and into the rooms to be heated 
at all times. A small volume of highly heated air is not only 
uncomfortable but unhealthful as well. 

2. There should be no cross-currents of air. The cold air 
from all parts of the house should join in a single current 
when returning to the furnace. (Study Figs. 84 and 85.) 

3. The heated air should enter at the warmest portion of 
the room and the cold air should be drawn out from the coldest 
portion. 

4. All of the air in all of the rooms to be heated should be 



DEVELOPMENT OF HOUSE HEATING 115 

in constant circulation, and all of the air should be heated 
to a comfortable temperature. 

5. A successful furnace does not overheat the basement. 
A furnace should have such a perfect circulation that the 
jacket never becomes very hot. The purpose of the furnace 
is to send heated air into the rooms above and not to heat 
the basement. 



Hot Water Heating 

122. Principles of Heating by Hot Water. — In heating 
houses by means of hot water, we depend largely upon the 
same principles as in furnace heating. In the furnace we 
depend upon the heating of the air and the consequent ex- 
pansion of it to produce the circulation; so here also Ave de- 
pend upon the heating of the water and the consequent ex- 
pansion of it to produce the necessary circulation. 

The water heater is usually placed in the basement (Fig. 
86). The hot water flows from the highest point of the 
heater through the main flow pipes to the radiators placed 
in the various rooms. From the radiators, the cold water 
returns through the return flow pipes to the bottom of the 
heater. In passing through the radiators, the water heats 
tiem and they in turn heat the air in the rooms, producing 
convection currents precisely as the stove does. 

The water cannot be kept in circulation without some active 
force to keep it moving. It is easily seen that we have verti- 
cal pipes filled with hot water, and others filled with cold 
water. The cold water being the denser and therefore the 
heavier, and the pipes being connected both at the top and 
the bottom, the cold water is certain to fall to the bottom of 
the system and crowd the heated- water to the top. This 
means that the cold water sinks into the heater and that the 
hot water is forced up into the radiators. The water in the 
radiators soon become cool and the water in the heater soon 
becomes heated, thus the circulation is maintained. Notice 



116 THE PRODUCTION AND USE OF HEAT 

the slope, or pitch, as it is called, in the case of the horizontal 
pipes. Why should these pipes slope as they do? 

123. Essential Features of Any Hot Water Heating Sys- 
tem. — 1. In any system of hot water heating, the circulation of 
the water depends upon the unequal weight of two columns 
of water, one heated and one cold. The heater, the piping, 
and the radiators must be placed with this thought in mind 

2. Since water expands when heated and contracts when 
cooled, every hot water heating system must be provided 
with an expansion tank. This tank is to give the water a 
chance to expand when heated without bursting the pipes. 
(See Art. 15, Ex. 11.) 

3. Care must be taken that every portion of the heater, 
the pipes, and the radiators can be drained completely when 
not in use ; this will prevent freezing and bursting of pipes. 

4. Care must be taken that the water in the expansion tank 
and in the pipe leading to it does not freeze when the heater 
is in use; otherwise a severe explosion may occur. Why is 
this so ? 

124. Advantages of Hot Water Heating. — Many people 
regard the hot water system of heating as superior to any 
other system. When well installed and properly operated, 
it doubtless is cheaper to operate and gives a milder, and more 
even heat than is usually obtained from other systems. It 
is also possible so to install this system of heating as to give 
ample ventilation, but in such a case it is doubtful if it is 
less expensive to operate than a good furnace system pro- 
viding equal ventilation. This will be explained in Chap. V. 
The first cost of a hot water system of heating is considerably 
greater than that of furnace heating and slightly greater than 
that of steam heating, which will soon be considered. 

Sensible anu Insensible Heat 

125. The Factors of Heat Quality. — We are all more or 
less familiar with heat changes. If we place a hot iron in a 



DEVELOPMENT OF HOUSE HEATING 117 

pail of cold water, the water becomes heated and the iron 
cooled. The temperature of both the iron and the water soon 
become the same. All of the heat which goes out of the iron 
goes into the water. The change in temperature in each case 
indicates the change in heat quantity. But we know that, if 
we use more of the water the change in temperature of the 
water will be less ; or, if we use a larger piece of iron and heat 
it to the same temperature before placing it in the water, the 
water will be heated to a much higher temperature. The fact 
is that heat quantity is made up of three factors. Usually 
these factors are: (1) Change in temperature; (2) quantity 
of matter involved; (3) kind of matter (Art. 101). We shall 
see, however, that the three factors may be: (1) A change in 
the form or state of the matter; (2) quantity of matter; (3) 
kind of matter. 

126. Sensible Heat. — When the three factors involved in 
the heat quantity are change in temperature, quantity of 
matter, and kind of matter we say the heat is sensible heat, 
because it may be perceived by the senses. The heat units 
are based upon the measurement of sensible heat. Define 
1 B.t.u. and show that the last statement is true, likewise 
show that it is true by defining a Cal. or a cal. (Art. 102). 

127. Heat Necessary to Turn a Liquid into a Vapor. — We 
have seen that by applying heat to the paraffin in the candle 
wick, to the kerosene in the lamp, to the alcohol and water in 
the distilling flask we changed these liquids into vapors. In 
each case we put heat, a certain number of calories, or B.t.us. 
of heat, into the liquid to turn it into vapor. It takes a large 
amount of heat to turn water into vapor after it has been 
heated to the boiling temperature. We can get a fairly good 
idea of the amount required by performing an experiment. 

Exercise 39. — Amount of Heat Required to Vaporize Water 

Weigh a tin quart cup or small tin basin. Fill the eup half full 
of water and crushed ice or snow. Weigh again. Stir the water 
until the ice is just melted. The water should now be at 0°C. 
Quickly place the cup over a flame and note the exact time by the 



118 THE PRODUCTION AND USE OF HEAT 

watch. The height of the flame must not be changed during the ex- 
periment. "Watch the water till it begins to boil. Note the exact 
time again. Record the number of minutes required to bring the 
water to the boiling point. Allow the water to continue boiling 
about twice as long as was required to bring it to the boiling 
point. Now remove the flame and record the exact time. Weigh 
the vessel and contents again. 

Record your results as in the table below. 

Discussion of Exercise 39. — A student performing this 
experiment got the following record : 

Weight of 1-qt. tin basin 86 grams 

Weight of basin and water 309 grams 

Weight of the water alone 223 grams 

Began heating the water at 2-33-30 

Water began boiling at 2-42-40 

Time required to boil the water 9 min. 10 sec, or 550 sec. 

Let the water boil till 3-1-40 

Water boiled for 19 min., or 1140 sec. 

Weight of the basin and water after 

boiling 219 grams 

Therefore, weight of the water vapor- 
ized 90 grams 

From this record we see that it required only 550 seconds 
to raise 223 grams of water from 0°C. to 100°C.; but that it 
required 1140 seconds, while applying thp same heat, to vapor- 
ize 90 grams of water. Now 90 grams was but 9 %23 of the 
whole amount of water or 0.403 of it. To have evaporated 
all of the water would have required 1140 seconds -=- 0.403 or 
2828 seconds. From this experiment w 7 e conclude that it re- 
quires 2S2 %50 times, or 5.14 times, as much heat to vaporize 
a certain quantity of water as is required to raise that 
quantity of water from the freezing point to the boiling 
point. 

Very careful experiments repeated many times have proved 
that these figures should be 5.36. Heat which is used thus 
to change the state of matter without changing its tem- 
perature is called insensible heat. When used to change a 



DEVELOPMENT OF HOUSE HEATING 



119 



liquid to a vapor, it is called heat of vaporization. When 
used to change a solid into a liquid, it is called heat of 
fusion. We now see that the heat of vaporization of water 
is 5.36 times the sensible heat of raising the same amount of 
water from the freezing point to the boiling point. 

Steam Heating 

128. Principles of Steam Heating. — "We saw in Arts. 20 

and 21 that the temperature of steam arising from boiling 

water is nearly the same as that of the water. It is also known 

that as long as the pressure remains constant the temperature 




Fig 87. — System of piping for steam 
heating. 

of the steam remains the same. In Art. 127, Ex. 39, we saw 
that a large amount of heat must be put into water to turn it 
into steam. When the steam is again turned into liquid, 
i.e., liquefied, exactly the same amount of heat is given off 
as was absorbed in the vaporizing. Steam heating depends 
upon an application of these principles. 

129. Equipment for Steam Heating. — As in the case of hot 
water heating, the equipment consists of a heater, generally 
called boiler, of connecting pipes, and radiators (Fig. 87). 
In fact, a plant for hot water heating may be, and some- 
times is, used for steam heating with but slight modification. 



120 THE PRODUCTION AND USE OF HEAT 

This is so, notwithstanding the fact that the two systems are 
very different in principle. 

130. Hot Water and Steam Systems Contrasted. — The two 
systems may be contrasted as follows : 

1. In the hot water system, the radiator is heated by re- 
ceiving the sensible heat given off by the water as it is 
cooled in passing through the radiator. 

In the steam system, water is turned into steam in the 
boiler. The steam then passes up through the pipes to the 
radiator and is there condensed, giving off its heat of vapori- 
zation. This is the source of the heat which keeps the radi- 
ator hot. The hot water, condensed steam, returns to the 
boiler, often at 100°C. 

2. In the hot water system, the water is kept in circulation 
by its own unequal density. The hot water, being lighter, is 
pushed upward into the radiator while the colder, heavier 
water sinks into the heater, crowding the hot water upward. 

In the steam system, the steam is forced upward into the 
radiators by the unequal pressure upon it. In the boiler, 
more water is constantly being changed into steam, tending 
thereby to increase the pressure. In the radiator, the steam is 
constantly condensing into water, tending thereby to decrease 
the pressure. This means that there is always a lower pres- 
sure in the radiator than in the boiler, and consequently, 
steam is constantly being forced from the boiler into the 
radiator. 

3. In the hot water system, the heater, the pipes and the 
radiators are always completely filled with water. 

In the steam system, the boiler is but partly filled with 
water. 

4. The ordinary hot water system is never closed but always 
open at the expansion tank. 

The steam system is always closed but the boiler must be 
provided with a safety valve (Art. 134). 

5. Hot water heating and furnace heating are generally 
used in small or medium sized buildings where all of the 



DEVELOPMENT OF HOUSE HEATING 



121 



rooms to be heated are above the heater or furnace and not 
far removed from it. They do not give good results when 
long horizontal pipes must be used. 




Fig. 88. — A steam heating plant. The steam trap and reducing valve 

are enlarged. 

131. A Steam Heating Plant. — Steam heating is especially 
adapted to the heating of large buildings and rooms which are 
considerably removed from the boiler (Fig. 88). In many 
cities large, central steam heating plants are constructed. 



122 THE PRODUCTION AND USE OF HEAT 

Steam pipes extend from the plant throughout large portions 
of the city. These pipes are supported within brick con- 
duits beneath the surface of the street. Smaller supply pipes 
lead from the mains to the business blocks and the residences 
on either side of the street. Steam heat is then sold to cus- 
tomers just as gas (Art. 48) and water (Art. 502) are sold. 

Exercise 40. — A Study of Fig. 88 

The boiler is a fire-tube boiler. Compare this boiler with that 
shown in Fig. 73. How do the two boilers differ? At what pressure 
does the steam pass from the boiler to the reducing valve? Under 
what pressure is the steam in the radiators? The radiators are 
usually of east iron and are not made strong enough to stand safely 
high pressure. Examine carefully the reducing valve and explain 
how it works. What would be the effect of moving the iron ball 
farther out on the lever? Study carefully the picture of the steam 
trap and explain how it works. The ball within the trap is hollow 
and very light. What happens as the water accumulates in the 
trap? Just what is the purpose of the steam trap? What would 
happen if no steam trap were used? 

132. Safety Devices on Steam Boilers. — All steam boilers 
are equipped with three safety devices, a pressure ga^e (Art. 
133), a safety valve (Art. 134), and a water gage (Art. 135), 
for it is necessary, first, that the operator shall be able to 
see at once what pressure the boiler is carrying, second, that 
under no condition shall the steam pressure become greater 
than that which the boiler is intended to carry, and third, 
that the water in the boiler never gets below a certain level. 

133. The Pressure Gage. — The purpose of the pressure 
gage is to indicate the steam pressure on each square inch 
of the boiler. Its essential parts are: (1) A curved, somewhat 
flexible, metallic tube, A, Fig. 89 ; this tube is connected by 
a small pipe to the boiler; (2) hinged to the free end of the 
curved tube is a short connecting rod, B ; the other end of the 
rod is hinged to one end of the lever C; the opposite end of 
the lever C carries a circular set of cogs; (3) these cogs on 



DEVELOPMENT OF HOUSE HEATING 



123 



the end of the lever C mesh into the cogs on the cog wheel, 
D, which carries the pointer or index. 

As the steam pressure rises with- 
in the boiler, the pressure tends to 
cause the curved tube to straighten 
out. The tube then pulls up on 
the rod. The rod lifts the 
right-hand end of the lever. The 
cogs at the other end of the lever 
cause the cog wheel to rotate clock- 
wise. The index points to a scale 
printed on the face of the gage. 
There is always 1 atmosphere of 
pressure on the exterior of the 
boiler. Now the pressure gage in- 
dicates the excess of pressure, i.e., 
the pressure over and above 1 atmosphere, on the inside of 
the boiler. 

134. The Safety Valve. — Safety valves are of two types: 
The ball and lever type and the pop valve type. In the 




Fig. 89. — The pressure gage. 





Fig. 



90.— Ball and lever, 
safety valve. 



Fig. 91.— Pop safety 
valve. 



ball and lever type, Fig. 90, the valve is held clown by the 

weight of the ball upon the lever. The pressure is increased 

by slipping the ball farther out on the lever. Explain why. 

The principle of the pop valve is shown in Fig. 91. The 



124 THE PRODUCTION AJMD USE OF HEAT 

valve in this case is held down by a spiral spring. The top 
of the spring rests against a metal washer. This plate may 
be forced farther down by turning down the screw. The 
spring then holds the valve down against a greater pressure. 
In each type, the valve opens and allows some steam to escape 
as soon as the pressure within the boiler exceeds the amount 
for which the valve is set. 

135. The Water Gage. — The purpose of the water gage is 
to enable the operator or engineer to see exactly how high the 
water stands in the boiler. The gage is merely a strong 
glass tube mounted on the side of the boiler at the height at 
which the water should stand. This glass tube is so connected 
at both its top and its bottom that the water stands within 
it at the same height as it stands within the boiler. This 
gage is of the greatest importance, for the person in charge 
must never permit the water within the boiler to get lower 
than the bottom of the gage. The danger from an explo- 
sion is very great if the water is permitted to get too low in 
the boiler. Point out the water gages on the boilers shown 
in the illustrations (Figs. 88 and 309 and 310). 

The Open Grate 

136. The Low Efficiency of the Old Fireplace. — The old 

colonial fireplace was of immense size, often 6 or 8 ft. in 
width, and consumed immense quantities of fuel. Still the 
room was but poorly heated. The burning logs resembled a 
huge bonfire and the draft up the chimney was intense. To 
replace the large amount of air which passed up and out of 
the chimney, a blast of cold air poured in at every crack and 
crevice. A cold current was always crossing the room from 
the outside wall to the chimney. Probably nine-tenths of 
the heat was swept up and out of the chimney without warm- 
ing the room at all. Only a little of the heat passed back 
into the room, and that was by radiation. It is an old say- 
ing that the old-fashioned fireplace roasted one side of a 
person while the other side froze. (Art 66). 



DEVELOPMENT OF COOKING DEVICES 125 

137. The Common Modern Grate. — The common grate of 
today is not used extensively in the northern states for heat- 
ing purposes. It is generally regarded as a secondary heat- 
ing plant to be used in the fall and spring or in conjunction 
with some other system of heating in the winter. In the 
southern states, where little artificial heat is needed, it is often 
the only heating plant. 

The modern grate consumes but little fuel compared with 
the old-time fireplace. The flue is much smaller and the 
amount of air passing up the chimney far less. The "roast- 
ing and freezing" effect is not nearly so marked as in the 
case of the old-fashioned fireplace. Still the efficiency is very 
low. Usually not more than 12 or 15 per cent, of the heat 
generated is utilized in heating the room in which the grate 
is placed. But even then, this common grate is invaluable 
from a sanitary point of view as will be shown later when 
considering ventilation (Chap. V). 

X. DEVELOPMENT OF COOKING DEVICES 

Stoves and Ranges 

138. Cooking Before the Days of Stoves. — Throughout 
the 18th century and until well into the 19th, cooking stoves 
were unknown in America. Most of the food was cooked 
by boiling in pots which hung suspended from the swinging 
crane in the fireplace. Some articles of food, such as apples 
and potatoes, were roasted in the coals upon the hearth. 
Meats were generally roasted by being suspended by means 
of a cord or wire before the fireplace. In order that the 
meat be made to roast evenly it had to be turned almost 
constantly. This was usually a child's task in the private 
family. In many inns, where much meat had to be roasted, 
it was often mounted upon a spit, or sharpened stick of wood, 
in such a manner that it could be kept turning constantly, 
often by means of a tread mill operated by a dog. Figure 
92 shows an ingenious device used in the London Club House, 



126 



THE PRODUCTION AND USE OF HEAT 



a fashionable hotel in London. The fire was built on a 
series of grates standing in front of a wrought-iron water 
heater. Before the several grates were horizontal spits upon 
which the meats to be roasted were placed. These spits 
were caused to revolve by the " smoke jack," a small metal 
wind mill mounted in the chimney flue. 

One of the most frequently used utensils for cooking was 




Fig. 92 



Fig. 93 



Fig. 92. — The kitchen fireplace at the City of London Club House, 
Broad street, London. Reproduced from an old wood cut. The "spits" 
upon which the joints of meat were mounted before the fire were kept 
revolving by a "smoke jack," a small windmill, mounted in the chim- 
ney flue. 

Fig. 93. — Reflector formerly used for roasting and baking in the home. 



the reflector. It was a semi-cylindrical box made of bright 
tin and so mounted that it lay upon one side (Fig. 93). Gen- 
erally it was equipped with a grate-like shelf upon which 
the meat could be placed, the juices dripping through into 
the bottom of the reflector below. The reflector was placed 
upon the hearth before the fire and was used, not only for 
cooking meat, but for baking as well. A modified form of the 



DEVELOPMENT OF COOKING DEVICES 



127 




reflector is shown in Fig. 94. A coiled spring in the box on 

the top of the reflector was wound up. The uncoiling of 

the spring was regulated by a sort of clock 

work. As the spring uncoiled, it revolved 

the spit upon which the joint of meat was 

mounted. 

The old brick oven built into the side 
of the fireplace, Fig. 59, is known to every 
one, and has a permanent place in our 
mental picture of an old-fashioned kitchen. 
As a matter of fact, however, it usually was 
heated and used one day in the week. A 
flue led from this oven into the chimney. 
On baking day, a wood fire was built in 
it and when it was sufficiently heated, the 
coals and ashes were raked and swept 
out and the week's baking placed in it. 

139. The Early Cook Stoves.— The 
first American stoves intended especi- 
ally for cooking were made about 1820. The Conant 
stove, made at Brandon, Vermont, was one of the 
first (Fig. 95). It was a cast-iron stove with firebox at the 
bottom. The oven was above the firebox and had doors open- 
ing both at the front and the rear of the stove. The smoke 
pipe went up through the oven. On each side of the stove 
was a projection which held a cast-iron kettle whose bottom 
was exposed to the heat of the fire. Most of the food was 
cooked by boiling in these kettles, although some baking 
was done in the oven. The stove had an ample hearth, and 
roasting was accomplished by opening the firebox door and 
placing the old style reflector upon the hearth. 

The Stanley rotary stove was made at Troy, New York, 
about 1835 (Fig. 96). It also had an ample hearth. Its top 
revolved by means of a crank and cogs. It carried five 
griddles of varying sizes. By revolving the top, any one 
of these griddle holes could be brought over the hottest part 



Fig. 94.— A re- 
flector for home 
use in which the 
"spit" upon which 
the joint of meat 
was mounted was 
kept constantly 
revolving by a 
coiled spring in a 
box on top of the 
reflector. 



12! 



THE PRODUCTION AND USE OF HEAT 



of the fire or placed in a cooler position as desired. The 
directions for using the stove read: "Roasting is done in the 
best manner by reflection in the tin oven under the stove 
(where it is to stand) and may at the same time be done on 
the front part of the stove in the common reflector which most 
families have." 

Another early stove was the "Yankee Notion" (Fig. 97). 
This was also a cast-iron stove. There were griddle holes 
on the top for kettles. At the rear of the stove arose a large, 
strong cast-iron pipe supporting the oven. The smoke and 
the products of combustion passed through flues around the 
oven and joined on top to enter the smoke pipe. 





Fig. 95.— The Conant 
stove; made at Brandon, 
Vt„ 1820. 



Fig. 96. — Stanley's rotary stove; made 
about 1835. 



While these stoves appear to us to be crude and very un- 
promising as cooking stoves, we should remember that they 
were considered very excellent by our grandmothers. 

140. Modern Cook Stoves for Coal and Wood. — The modern 
cook stove for wood or coal differs from these early stoves in 
having its oven directly behind the fire-pot. Behind and be- 
neath the oven is a diving flue. This space is really divided 
into two flues side by side connecting at the front. When 
the oven damper is up as in the cut (Fig. 98), the smoke 
and the products of combustion must pass downward behind 
the oven, forward beneath the oven, around the end of the 
partition, thence backward again and upward to the pipe. 
This heats all around the oven except the two sides. 
Usually there are doors in both sides of the oven. When the 



DEVELOPMENT OF COOKING DEVICES 



129 



oven damper is down, the products of combustion pass directly 
from the fire-pot over the oven and up the pipe. Examine a 
stove carefully to note the flues and see how they may be 
cleaned. 

141. The Range. — A stove which was so arranged as to fit 
easily into a fireplace was called a range. This term is still 
applied to a stove which has one of its long sides for the front 
and the other for the back. In the range, the oven flues are 
usually so constructed that the products of combustion pass 
downward at the side of the oven, then circle beneath the oven 
and up to the pipe which is connected at the center of the 





Fig. 97. — The Yankee no- 
tion: about 1835. 



C **1^a*j£T»W/to^ 



Fig. 98. — Common cook stove. 



back of the range. The oven is thus heated on all sides but 
the front. Examine a range carefully to note the flues and 
see how they may be cleaned (Fig. 99). 

142. The Gas Range. — The gas range is a stove constructed 
to burn natural gas, coal gas, water gas or other gaseous fuels. 
Since the object is to burn the gas under such conditions as 
to produce heat and not light, the flame must be non-luminous. 
This means that the gas must be mixed with air in a mixer 
before it enters the burner, just as the gas must be mixed with 
a sufficient amount of air in the mixer of the incandescent 
gas lamp (Art. 50). Therefore, on every gas stove or gas 
range there is a mixer into which the gas passes on its way 
to the burner. The mixer is supplied with some device for 



130 THE PRODUCTION AND USE OF HEAT 

controlling the amount of air which enters and mixes with 
the gas. 

Exercise 41. — Regulating the Air Supply of a Gas Stove 

Examine a gas stove carefully, noting the air regulator usually 
at the front of each burner. Note carefully how the supply of air 
is regulated. Shut oft' the air supply from one burner. What is 
the effect upon the flame? Why does it become a luminous flame? 
Reopen the damper slowly, noting just the amount of air necessary 
to produce a non-luminous flame. Notice that more air is required 
to produce a non-luminous flame when the gas is turned on full 
strength than is required when the gas is partly turned off. 




Fig. 99. — A range. 

The most intense, i.e., the hottest, flame is secured when 
the damper is so set that there is just a sufficient amount of 
air to produce a non-luminous flame. An excess of air not 
only reduces the intensity of the heat, but it also tends to cause 
the flame to "strike back," i.e., to burn down in the burner 
instead of above the burner as it should. If the supply of 
air is insufficient, the flame will be luminous and smoky. 

The air supply on a gas stove should be carefully watched 
and frequently regulated to secure the best results. 

Fireless Cookers 

143. Cooking Temperatures. — The cooking of foods is ac- 
complished by raising them to a certain temperature and then 



DEVELOPMENT OF COOKING DEVICES 



131 



maintaining that temperature for a certain length of time. 
Both the temperature required and the time required vary, 
first, with the nature of the food to be cooked, and second, 
whether it is to be cooked wet, i.e., stewed or boiled, or 
cooked relatively dry i.e., baked. "Stewing" and "boiling" 
usually require a temperature near the boiling point of water, 
or from 180° to 212 °F. Baking requires a much higher 
temperature. Bread is commonly baked at about 375°F. 

144. Conductors and Non-conductors. — If it were possible 
to discover a device which would entirely prevent the loss of 



If) STOP ON BAi 




ALUMINUM BAND ABOUND 8AKING ANO. 
BOASTING OlSKS / 

Fig. 100. — A lireless cooker. 

heat, it is evident that it would be necessary only to bring the 
food once to the proper temperature; if no heat were lost, 
the food would then remain at that temperature indefinitely 
or until cooked. Unfortunately we know of no means of 
preventing heat from escaping through the walls of any 
vessel we can construct. Heat passes through every known 
material. However, it passes through some materials much 
more readily than through other materials. Materials 
through which heat passes readily are said to be good con- 
ductors of heat; materials through which heat passes less 
readily are said to be poor conductors of heat. All metals 



132 THE PRODUCTION AND USE OF HEAT 

are good conductors of heat ; air, asbestos, and paper are poor 
conductors. 

145. Fireless Cookers. — Fireless cookers are constructed 
of materials which are poor conductors. They are usually 
vessels of box-like construction with thick walls constructed 
of poor conductors and provided with closely fitting covers 
of similar construction (Fig. 100). The food to be cooked is 
usually brought to the desired temperature and then quickly 
placed in the fireless cooker. The cooker largely prevents 
the loss of heat; therefore the food may be maintained for 
many hours at an approximately constant temperature. A 
fireless cooker intended for baking is usually provided with 
one or more blocks of soapstone. These are cut to fit the 
cooker. Soapstone is used because of its great capacity of 
holding heat, i.e., its high sensible heat (Art. 126). When 
baking is to be done, the soapstone is heated to a high tem- 
perature and placed in the cooker with the article to be baked. 
The temperature of the interior of the cooker is soon raised 
to the temperature necessary to bake the food. 

The chief purpose of fireless cookers is to save fuel. They 
are very successful, and, when properly handled, they effect a 
considerable saving of fuel and at the same time lighten the 
labors of cooking, since they require little or no attention 
while the cooking is in progress. 



CHAPTER III 

THE WEATHER 

146. Why Study the Weather? — Weather is the condition 
of the atmosphere. It includes heat, cold, moisture, rain, 
snow, sunshine, cloudiness. The weather in the past has 
crumbled the rocks, formed the soil, watered the fields. In 
that way it has largely determined where food crops and food 
animals could be grown ; and thus it has largely controlled the 
growth of nations and the progress of the human race. The 
weather also affects the health and comfort and enjoyment and 
the outdoor occupations of all people every day. An un- 
derstanding of the weather enables one to safeguard his 
health, protect his property and manage his outdoor business 
or recreation more successfully. 

147. Beginnings and Growth of Weather Knowledge. — 
We do not know when man commenced to watch the weather ; 
but some of the sayings and proverbs about the weather date 
back more than 6,000 years. The ancient Hindus measured 
the rainfall; the Chaldeans named the wind directions; the 
Greeks kept records of the wind, and one of their philosophers, 
500 b. c, made an instrument that showed changes in tempera- 
ture. The modern thermometer and barometer were not in- 
vented until the 17th century; then explorers soon began 
carrying thermometers on their journeys to measure the tem- 
peratures they found in different lands. About 150 years ago 
men began to understand a little of the laws governing the 
weather. Today, in all the leading countries, there are men 
whose business it is to watch the weather and to see what is 
coming in the next day or two. And many people and many 
lines of business plan their work or their affairs according to 
the expected weather. 

133 



134 THE WEATHER 

(In the recent great war, scores of men on each side took regular 
observations of the weather. Each important army had trained 
forecasters who received those weather observations and told the 
commanders, as fully as possible, when clouds or fog, rain, snow, 
haze and changes in humidity were coming, and how the winds 
would blow both on the ground and high in the air. This was done 
to help the armies in bombing raids, air fighting, the photographing 
of enemy lines from airplanes and balloons, for gas warfare, for 
making surprise attacks, for the moving of troops and supplies, for 
the aiming of long-range cannon, and other operations of the armies. 

As airplanes come to be used more, the weather will need careful 
and constant watching in order to make flying safest and easiest 
and least expensive.) 

Almost anyone can learn something of the weather, and 
will find the knowledge interesting and useful. To study the 
weather best, we begin with our own. 

I. METHODS OF STUDYING THE WEATHER 

148. Observing Weather Without Instruments. — Can you 
describe yesterday's weather in your locality? Do so. Was 
the day clear or cloudy? Was it warm or cold for the sea- 
son ? What was the direction of the wind ? Was it strong or 
light? Did it change direction during the day? Did you 
notice the clouds? What direction were they moving? If 
there was rain or snow, when did it fall ? Was the fall heavy 
or light? Describe today's weather fully, giving all changes 
that have occurred since morning. 

Such features as the amount of rain, the exact temperature, 
or the speed of the wind, can best be measured and recorded 
by instruments; and some of those instruments will be 
studied soon. But an interesting and useful record of many 
weather conditions can be made without instruments. Such 
records are kept at all weather stations. 1 

1 To the Teacher : The class should keep a record of, and study 
their local weather for at least two or three weeks in September or 
early October, two weeks in midwinter, and two or three weeks in late 
April or May, in order to become better acquainted with the weather 
of the different seasons. 

After the study of general storms, the daily weather maps should 
be studied each day in connection with your local weather. 



METHODS OF STUDYING THE WEATHER 



135 



Exercise 42. — Daily Observations without Instruments 

Keep a record like the following. Observe the weather about 
9 A. M. and 4 p. m. if practicable. 



Date 


Hour 


Clouds 


Tem- 
pera- 
ture 


Thermom- 
eter 
degrees 


Wind 


Remarks 


Indica- 
tions 


Sept. 1 
Sept. 1 
Sept. 2 


9 a.m. 
4 p.m. 
9 a.m. 


1/3 dark-low 
Cloudy, heavy 
%high 


Warm 
Cooler 
Cool 


80 
70 
62 


Brisk-^ 
High-V 
Mod.-^ 


Thunderstorm 
Rain ended 
in night 


Showers 

Rain 

Clearing 



For clouds, express the portion of sky covered, by the appropriate 
word from group "a" below; for color or appearance, use words in 
group u b"; for elevation, use "c" words. Record the temperature as 
it seems to you, whether warm or cool, etc., for the time of year. 
Record the exact temperature if you have a thermometer. 

Record the wind direction by arrows flying with the wind. Call 
the top of the page north, the right side (your right as you face it) 
east, etc. Record as follows: 

Light, when just moving the leaves of trees. 

Moderate, when just moving small branches. 

Brisk, when swaying large branches. 

High, when swaying entire trees and picking papers 

and dust up from the ground. 
Gale, when breaking small branches and damaging 

light buildings. 

Under "Remarks" note any special features. 

The following groups of words may be used in the proper col- 
umns of the record, to express the conditions : 



Clouds 



(a) (6) 

Clear Light clouds 

Few clouds Dark clouds 
}£ cloudy (c) 

% cloudy Low clouds 
Cloudy High clouds 

Heavy clouds 



Temperature 


Wind 


Remarks 


Very warm 


Calm 


Raining 


Warm 


Light 


Snowing 


Moderate 


"Moderate 


Sleeting 


Cool 


Brisk 


Threatening 


Cold 


High 


Storm clouds 


Very cold 


Gale 


Thunderstorm 



136 THE WEATHER 

The class should continue this record while they are learn- 
ing to use weather instruments. Study your record carefully 
once each week and write answers to as many of the following 
questions as you can : 

1. Does the sky appear to be more or less cloudy for the few hours 
preceding a storm? How is it for the few hours after the storm? 

2. Is there any direction from which the wind blows frequently 
before a storm? If so, what direction? Is there any direction from 
which it blows most frequently after a storm? 

3. Does the wind increase, or decrease, in the few hours before a 
storm? Does it blow harder before, or after, a storm? 

4. Does the temperature seem warmer, or colder, before a storm? 
How does it change after a storm, if at all? 

II. THE USE OF WEATHER INSTRUMENTS 

Most persons know something of the thermometer and how 
to use it. Some have seen or used a raingage. The barometer, 
which measures the pressure, or weight, of the air, is the most 
important of weather instruments. We shall study it first. 

149. The Measurement of Air Pressure; Air Has Weight. 
— When compared with any common liquid or solid, air is so 
light that it seems to have no weight. Yet smoke rises 
through the air, and balloons ascend out of sight. This is 
possible only because air is heavier, or denser, than the smoke 
or the gas in the balloon and crowds them upward, just as a 
cork rises to the surface of water because water is heavier, 
or denser, than cork and crowds it upward. But we can 
not see the air; we scarcely feel it; we seldom think of it. 
That such a substance constantly surrounds us, filling every 
nook and corner of our houses, even penetrating deep into 
the ground itself; that it is constantly pressing with great 
force upon our bodies — these things many of us have not 
realized. 

It was not until 250 or 300 years ago that even men of 
science began to understand that air is a real substance and 
has weight as truly as has water or stone or iron. About 



THE USE OF WEATHER INSTRUMENTS 137 

1630, Galileo made the first attempt to find the weight of 
air. He weighed a flask filled with air, then removed part 
of the air by heating the flask just as we did in Ex. 36, 
Art. 111. He sealed the flask while hot and then weighed 
it again. Since this method removed but part of the air, 
he placed the mouth of the inverted flask in water, unsealed 
it, and lowered it as it filled with water. He then closed the 
mouth and lifted the flask from the water. The volume of 
water remaining in the flask equaled the volume of air re- 
moved by the heating. 

About 25 years later, Guericke constructed the first air 
pump. After that, the air could be removed by the pump. 
But no air pump will remove all of the air, and today when 
this experiment is performed, we must find some means of 
discovering how much air has been removed from the flask. 

Exercise 43. — Weighing Air 

Fit a 2-qt. or 4-qt. bottle with a new one-hole rubber stopper 
through which passes a short glass tube. To the glass tube attach 
about 2 ft. of rubber tubing. 1 Fit the rubber tubing with a screw 
clamp. Now weigh the bottle full of air with all attachments, using 
trip scales. Attach the rubber tube to the air pump, 
making sure that all joints are tight. Vaseline the joints if neces- 
sary. Pump as much air as possible out of the bottle; close the 
rubber tube tightly with the screw clamp ; detach the tube from the 
pump and quickly weigh the bottle and fittings. Place the tube and 
mouth of the bottle under water and open the screw clamp. The 
bottle quickly fills nearly full of water. Why? Hold the bottle so 
that the water inside and outside is on a level. Close the tube and 
lift the bottle from the water. Pour the water from the bottle into 
a measuring graduate and record the volume. This volume is the 
same as that of the air removed from the bottle. Compute the 
weight of 1 liter, 1000 c.c, of air. 

A student performing this experiment obtained the following re- 
sults (metric system) : 

Weight of bottle full of air 786.2 grams 

Weight of bottle after removal of air. . . 784.8 grams 



1 Note : Thick-walled or pressure tubing should be used. 



138 THE WEATHER 

Therefore, weight of air removed 1.4 grams 

Volume of water in the bottle 1150 c.e. 

From these facts he computed the weight 

of 1 liter of air to be nearly 1.22 grams 

Prove the correctness of his computation. 

Air varies much in weight at different times and places. 
Cold air is heavier, or denser, than warm air, and moist air is 
lighter, or less dense, than dry air. At sea level, dry air 
weighs about 1.29 grams per liter, or about l 1 /^ oz. per cu. ft. 
About 13 cu. ft. of air weigh 1 lb. 

150. Air Pressure. — Though a cubic foot of air weighs but 
little, the atmosphere is many miles deep and presses with 
great force upon all the earth's surface. This fact was dis- 
covered soon after it was found that air has weight. 

Exercise 44. — To Study the Pressure of Air 

(a) Place a palm glass upon the stand of the air pump. Place 
rubber dam over the mouth of the palm glass and tie its edges down 
tight with a cord. Connect the stand with the pump. With the 
first stroke of the pump notice the effect on the rubber dam. If 
the rubber is fresh and strong, continued pumping may stretch it 
till it very nearly lines the inside of the receiver. 

(b) Tie the rubber dam over the mouth of a thistletube. Attach 
a rubber tube to the stem of the thistletube. Suck some of the air 
from the tube and note how the dam is pressed into the tube's mouth. 
Pinch the tube so that air cannot enter; then hold the thistletube 
with its mouth upward, downward, sidewise. May we conclude that 
air pressure is equal in every direction? 

The total air pressure upon our bodies is many hundreds 
of pounds. We *do not feel it, because the air enters our lungs 
and thus exerts the same pressure on both the inside and 
outside of our bodies. These pressures balance each other. 

151. Torricelli's Experiment. — Galileo, who proved that 
air has weight, also noticed that a pump in a deep well raised 
the water only about 32 ft. All scientists before him had 
taught that "Nature abhors a vacuum." Galileo remarked, 



THE USE OF WEATHER INSTRUMENTS 139 

when observing the pump, that nature's abhorrence seemed 
to stop at 32 ft. His experiments 
in search of the explanation were 
ended by his death in 1642. Torricelli, 
his pupil, at Galileo's request, con- 
tinued the investigation. Torricelli con- 
cluded that air pressure had something 
to do with the action of the pump. 
He remembered that mercury is 13.5 
times as heavy as water; he reasoned 
that if the air pressure raised water 
32 ft. in the pump, it would raise or 
support mercury % 3 . 5 as high, or about 
29 in. He experimented and proved 
his theory. One of his experiments, 
first performed in 1643, is often re- 
peated today. 




Fig. 101.— Torri- 
celli's experiment. The 
tube is shortened very 
much in the illustra- 
tion. 



Exercise 45. — Torricelli's Experiment 



Fill it 
Pour 
Place 



Secure a glass tube about 36 in. long, closed at one end. 
with mercury, working over a pan to catch spilled mercury, 
the remaining mercury into a glass or iron cup (Fig. 101). 
your finger firmly over the top of the glass tube and invert the tube 
carefully, putting the open end into the mercury in the cup. Re- 
move the finger. What happens? There is likely to be considerable 
air in the mercury column, which quickly rises as bubbles to the 
surface in the tube. To remove this air, slip your finger over the 
open end of the tube. Lift the tube from the cup and stand it up- 
right. Add mercury till the tube is full. Invert it again in the cup 
of mercury. Measure the height of the mercury in the tube above 
the surface of the mercury in the cup. This should be about 76 
cm., or about 29.9 in. at sea level, becoming less at higher altitude. 



152. Measuring the Atmospheric Pressure. — The pressure 
of the air on the surface of the mercury in the cup supports 
the mercury in the tube. The height of the mercury column 
thus shows the weight, or pressure, of the air; and we have 
come to speak of the pressure as being so many centimeters 
or inches, meaning that the pressure of the air holds a column 



140 



THE WEATHER 







■' 1 





Fig. 102. 



Fig. 103. 




Fig. 104. 



Fig. 102. — A. Siphon barometer. B. Device for adjusting the bar- 
ometer tube so as to bring the surface of mercury in the cistern to the 
proper height. 

Fig. 103. — Fortin's pattern barometer. 

Fig. 104. — Sectional view of the cistern of a Fortin's pattern bar- 
ometer. 



THE USE OF WEATHER INSTRUMENTS 141 

of mercury that high. (Another way of expressing the pres- 
sure is in pounds per square inch, or in grams per square 
centimeter.) 

153. The Barometer. — The common mercury barometer is 
a mounted Torricellian tube having a scale for measuring 
the height of the mercury column. The cheaper "siphon" 
type (Fig. 102) has the lower end of the tube bent upward 
forming a cistern to hold the mercury. The Fortin pattern 
(Fig. 103) is more accurate. In it the tube is straight; the 
sides of the cistern are metal and glass; the bottom is stout 
buckskin (Fig. 104) and is supported by a metal plate which 
can be raised or lowered by a screw. Extending down from 
the top of this cistern is an ivory point, P. The scale near 
the top of the barometer is so placed that the line "26 in.," 
for instance, is exactly 26 in. above the tip of this ivory point. 

To read the barometer, first turn the screw s, at the bottom 
so that the top of the mercury in the cistern just touches the 
ivory point. Then read the height of the top of the mercury 
in the column above. To do that, turn the thumbscrew at the 
side to move the slide so that the bottom o % f the slide is just 
even with the middle of the curved top of the mercury. 
Then notice carefully where the bottom of the slide comes on 
the fixed scale at the side. Practice by moving the scale so 
that its bottom is exactly at 29.0 inches, then at 29.1, 29.2, 
and each other tenth to 30.0 inches. Next, place the bottom of 
the slide midway between the tenths, at 29.05, 29.15, 29.25, 
etc., until that is easy to do correctly. (Pay no attention yet 
to the marks on the slide itself.) Then go back to 29.15 and 
carefully see where you would move the scale for 29.17, 29.18, 
29.19, etc. Practice until you can read the scale accurately 
and quickly to two decimal places, at any portion of the scale. 

154. Correcting the Barometer Reading for Tempera- 
ture. — Mercury expands when heated (as in thermometers, 
Art. 15). If, on a cold winter day two barometers be hung, 
one just outside of a window and one just inside of the win- 
dow in a warm room, the one within the room will read con- 



142 THE WEATHER 

siderably higher than the one outside. The air pressure sup- 
ports the column of mercury. When the mercury is warm, 
and therefore lighter, it requires a higher column to balance 
the air pressure than when the mercury is cold. 

In order to compare the air pressures as indicated by bar- 
ometers on warm days and cold days, or at different places 
where the temperature differs, it is necessary to correct the 
readings for temperature. This is done by subtracting the 
proper amount from the reading for temperatures above 
28 1 /2°R Since barometers are nearly always kept indoors, 
and therefore warm, it will not be necessary to consider tem- 
peratures lower than 50°F. nor above 100° F. Table V 
(see p. 145) gives the necessary temperature corrections. 

Directions for Using Table V. — Notice that the table has a 
column for each half inch of the barometer from 24 to 31 in. At 
the left side is a temperature column. If the barometer reads 29.42 
in. and its attached thermometer reads 68°, find the barometer col- 
umn with heading nearest to 29.42 (in this case the 29.5 column); 
then follow that column down to the horizontal line running across 
from "68°." Where that line crosses the barometer column you 
find "0.10." This means that 0.10 in. must be subtracted from the 
barometer reading as a correction for temperature. The corrected 
reading is therefore 29.32 in. 

155. Correcting the Barometer for Altitude.— Since the 
barometer shows the weight or pressure of the atmosphere, it 
is evident that it will read highest when at the bottom of the 
atmosphere. The higher up into the atmosphere we carry a 
barometer, the less air there is above to press upon the 
mercury, and the lower the barometer will read. This fact 
was discovered soon after Galileo found that air had weight. 
Pascal, a Frenchman, heard of Torricelli's experiment in 1644. 
After several years of experimenting, Pascal concluded that 
the mercury in the tube would stand lower on a mountain 
top than at its base. He carried a tube to the top of a high 
tower and noticed a slight drop in the mercury column. He 
then asked his brother-in-law, who lived near the Puy de 



THE USE OF WEATHER INSTRUMENTS 



143 



Dome, a mountain in southern France, to carry a barometer 
to the summit of the mountain. This Perier did on Septem- 
ber 19, 1648, and Pascal's theory was confirmed (Fig. 105). 




o-SEA LEVEL— o- 



Fig. 105. — Atmospheric pressure varies with altitude. A shows 
elevation of New Orleans, (8 ft.); B, of Oklahoma, 1150 ft.; C, of 
Denver, 5600 ft. Barometer readings must be corrected for altitude 
before they can be compared. 

The barometer is used in studying the weather. Barometer 
reading's at sea level are ordinarily about 30 in. ; at the alti- 
tude of Chicago, about 29.4 in. ; at Denver, about 23 in. ; and 
at the top of Pike's Peak, about 15 in. Scarcely any two 
weather stations have the same elevation. Therefore, in order 
to compare barometer readings with those of other weather ob- 
servers, all readings must be corrected for altitude as well as 
for temperature. In doing this it is customary to change all 
readings to what they would have been if the barometer 
had been at sea level. These corrections are easily obtained 
from Table YI. (See p. 146). 

Directions for Using Table VI. — The proper correction is found 
from Table VI in a manner similar to that followed in using Table 
V. This correction, however, is added to the barometer reading. 

Note. — Extensive tables for the correction of barometers for any 
altitude from the sea level up to several thousand feet have been 
prepared. It is intended that the teacher or student wishing to use 
this book at an altitude not given in this table shall ascertain the 
corrections necessary at the required altitude and the various tem- 
peratures by applying to some nearby weather station, and record 
them on the line marked X. 



144 



THE WEATHER 



The corrected barometer readings everywhere in the United 
States will be exactly alike unless the actual pressure of the 
atmosphere differs in different places. We cannot see or feel 
differences in pressure as we do the differences in cloudiness 
or temperature or wind. But these differences in pressure 
cause most of the weather changes that occur. And if we 
write all the corrected barometer readings in their proper 
places on a map of the United States, we can see from the 




Fig. 106. — The barograph. 

map where storms are developing and where the weather 
will remain fair. This enables the Weather Bureau to make 
forecasts of coming weather. Barometers, used in that way, 
are the most important of weather instruments. 1 • 

156. The Barograph. — The barograph writes a continuous 
record of the barometer readings. The record paper is 
wrapped around a brass cylinder* that is turned by an eight- 
day clock. The barometer portion consists of a series of six 
or eight hollow elastic shells shaped like a canteen or two 
saucers turned top to top (Fig. 106). These shells are made 
of corrugated metal, soldered together one above the other, and 
the air has been exhausted from them. The atmospheric 

1 In addition to the pressure of the air, fully equipped Aveather sta- 
tions record the temperature, the rainfall and snowfall, the direction 
and force of the wind, the duration of sunshine and cloudiness, the 
amount of moisture in the air, and a number of other conditions. 
Several of these are recorded automatically by special apparatus. 



THE USE OF WEATHER INSTRUMENTS 



145 



Table V. — Reduction of Barometer Readings to 32°F. 

Corrections are to be Subtracted from the Reading of 

the Barometer 



So« 








Barometer reading in 


inches 










2.^1 3 




























g <u o 

Sis 


24.0 


24.5 


25.0 


25.5 


26.0 


26.5 


27.0 


27.5 


28.0 


28.5 


29.0 


29.5 


30.0 


30.5 


31.0 


50 


.05 


.05 


.05 


.05 


.05 


.05 


.05 


.05 


.05 


.05 


.06 


.06 


.06 


.06 


.06 


51 


.05 


.05 


.05 


.05 


.05 


.05 


.05 


.06 


.06 


.06 


.06 


.00 


.06 


.06 


.06 


52 


.05 


.05 


.05 


.06 


05 


.06 


.06 


.06 


.06 


.06 


.06 


.00 


.06 


.06 


.07 


53 


.05 


.05 


.05 


.06 


.06 


.06 


.06 


.06 


.06 


.06 


.06 


.06 


.07 


.07 


.07 


54 


.05 


.06 


.06 


.06 


.06 


.06 


.06 


.06 


.06 


.06 


.07 


.07 


.07 


.07 


.07 


55 


.06 


.06 


.06 


.06 


.08 


.06 


.06 


.06 


.07 


.07 


.07 


.07 


07 


.07 


.07 


56 


.06 


.06 


.06 


.06 


.06 


.06 


.07 


.07 


.07 


.07 


.07 


.07 


.07 


.07 


.08 


57 


.06 


.06 


.06 


.08 


.07 


.07 


.07 


.07 


.07 


.07 


.07 


.08 


.08 


.08 


.08 


58 


.06 


.06 


.07 


.07 


.07 


.07 


.07 


.07 


.07 


.08 


.08 


.08 


.08 


.08 


.08 


59 


.07 


.07 


.07 


.07 


.07 


.07 


.07 


.07 


.08 


.08 


.08 


.08 


.08 


.08 


.08 


60 


.07 


.07 


.07 


.07 


.07 


.08 


.08 


.08 


.08 


.08 


.08 


.08 


.08 


.09 


.09 


61 


.07 


.07 


.07 


.07 


.08 


.08 


.08 


.08 


.08 


.08 


.08 


.09 


.09 


.09 


.09 


62 


.07 


.07 


.08 


.08 


.08 


.08 


.08 


.08 


.08 


.09 


.09 


.09 


.09 


.09 


.09 


63 


.07 


.08 


.08 


.08 


.08 


.08 


.08 


.08 


.09 


.09 


.09 


.09 


.09 


.09 


.09 


64 


.08 


.08 


.08 


.08 


.08 


.08 


.09 


.09 


.09 


.09 


.09 


.09 


.10 


.10 


.10 


65 


.08 


.08 


.08 


.08 


.09 


.09 


.09 


.09 


.09 


.09 


.09 


.10 


.10 


.10 


.10 


66 


.08 


.08 


.08 


.09 


.09 


.09 


.09 


.09 


.09 


.10 


.10 


10 


.10 


.10 


.10 


67 


.08 


.08 


.09 


.09 


.09 


.09 


.09 


.09 


.10 


.10 


.10 


.10 


.10 


.11 


.11 


68 


.08 


.09 


.09 


.09 


.09 


.09 


.10 


.10 


.10 


.10 


.10 


.10 


.11 


.11 


.11 


69 


.09 


.09 


.09 


.09 


.09 


.10 


.10 


.10 


.10 


.10 


.11 


.11 


.11 


.11 


.11 


70 


.09 


.09 


.09 


.10 


.10 


.10 


.10 


.10 


.10 


.11 


.11 


.11 


.11 


.11 


.12 


71 


.09 


.09 


.10 


.10 


.10 


.10 


.10 


.10 


.11 


.11 


.11 


.11 


.11 


.12 


.12 


72 


.09 


.10 


.10 


.10 


.10 


.10 


.11 


.11 


.11 


.11 


.11 


.12 


.12 


.12 


.12 


73 


.10 


.10 


.10 


.10 


.10 


.11 


.11 


.11 


.11 


.11 


.12 


.12 


.12 


.12 


.12 


74 


.10 


.10 


.10 


.10 


.11 


.11 


.11 


.11 


.11 


.12 


.12 


.12 


.12 


.12 


.13 


75 


.10 


.10 


.10 


.11 


.11 


.11 


.11 


.12 


.12 


.12 


.12 


.12 


.13 


.13 


.13 


76 


.10 


.10 


.11 


.11 


.11 


.11 


.12 


.12 


.12 


.12 


.12 


.13 


.13 


.13 


.13 


77 


.10 


.11 


.11 


.11 


.11 


.12 


.12 


.12 


.12 


.12 


.13 


.13 


.13 


.13 


.14 


78 


.11 


.11 


.11 


.11 


.12 


.12 


.12 


.12 


.12 


.13 


.13 


.13 


.13 


.14 


.14 


79 


.11 


.11 


.11 


.12 


.12 


.12 


.12 


.12 


.13 


.13 


.13 


.13 


.14 


.14 


.14 


80 


.11 


.11 


.12 


.12 


.12 


.12 


12 


.13 


.13 


.13 


.13 


.14 


.14 


.14 


.14 


81 


.11 


.12 


.12 


.12 


.12 


.12 


!l3 


.13 


.13 


.13 


.14 


.14 


.14 


.14 


.15 


82 


.12 


.12 


.12 


.12 


.12 


.13 


.13 


.13 


.13 


.14 


.14 


.14 


.14 


.15 


.15 


83 


.12 


.12 


.12 


.12 


.13 


.13 


.13 


.13 


.14 


.14 


.14 


.14 


.15 


.15 


.15 


84 


.12 


.12 


.12 


.13 


.13 


.13 


.13 


.14 


.14 


.14 


.14 


.15 


.15 


.15 


.15 


85 


.12 


.12 


.13 


.13 


.13 


.13 


.14 


.14 


.14 


.14 


.15 


.15 


.15 


.15 


.16 


86 


.12 


.13 


.13 


.13 


.13 


.14 


.14 


.14 


.14 


.15 


.15 


.15 


15 


.16 


.16 


87 


.13 


.13 


.13 


.13 


.14 


.14 


.14 


.14 


.15 


.15 


.15 


.15 


.16 


.16 


.16 


88 


.13 


.13 


.13 


.14 


.14 


.14 


.14 


.15 


.15 


.15 


.15 


.16 


.16 


.16 


.17 


89 


.13 


.13 


.14 


.14 


.14 


.14 


.15 


.15 


.15 


.15 


.16 


.16 


.16 


.17 


.17 


90 


.13 


.14 


.14 


.14 


.14 


.15 


.15 


.15 


.15 


.16 


.16 


.16 


.17 


.17 


.17 


91 


.13 


.14 


.14 


.14 


.15 


.15 


.15 


.15 


.16 


.16 


.16 


.17 


.17 


.17 


.17 


92 


.14 


.14 


.14 


.15 


.15 


.15 


.15 


.16 


.16 


.16 


.17 


.17 


.17 


.17 


.18 


93 


.14 


.14 


.14 


.15 


.15 


.15 


.16 


.16 


.16 


.17 


.17 


.17 


.17 


.18 


.18 


94 


.14 


.14 


.15 


.15 


.15 


.16 


.16 


.16 


.16 


.17 


.17 


.17 


18 


.18 


.18 


95 


.14 


.15 


.15 


.15 


.16 


.16 


.16 


.16 


.17 


.17 


.17 


.18 


.18 


.18 


.19 


96 


.15 


.15 


.15 


.15 


.16 


.16 


.16 


.17 


.17 


.17 


.18 


18 


.18 


.18 


.19 


97 


.15 


.15 


.15 


.16 


.16 


.16 


.17 


.17 


.17 


.18 


.18 


.18 


.18 


.19 


.19 


98 


.15 


.15 


.16 


.16 


.16 


.17 


.17 


.17 


.17 


.18 


.18 


.18 


.19 


.19 


.19 


99 


.15 


.15 


.16 


.16 


.16 


.17 


.17 


.17 


.18 


.18 


.18 


.19 


.19 


.19 


.20 


100 


.15 


.16 


.16 


.16 


.17 


.17 


.17 


.18 


.18 


.18 


.19 


.19 


.19 


.20 


.20 



146 



THE WEATHER 



Table VI.— Reduction op Barometer Readings to Sea Level 
Corrections are to be Added to the Reading of the Barometer 



1* 


Temperature of outdoor air in degrees Fahrenheit 


3- s 


20° 


10° 


0° 


10° 


20° 


30° 


40° 


50° 


60° 


70° 


80° 


90° 


100° 


20 


.03 


.03 


.03 


.02 


.02 


.02 


.02 


.02 


.02 


.02 


.02 


.02 


.02 


40 


.05 


.05 


.05 


.05 


.05 


.05 


.05 


.04 


.04 


.04 


.04 


.04 


.04 


60 


.08 


.08 


.07 


.07 


.07 


.07 


.07 


.07 


.06 


.06 


.06 


.06 


.06 


80 


.10 


.10 


.10 


.10 


.09 


.09 


.09 


.09 


.09 


.08 


.08 


.08 


.08 


100 


.13 


.13 


.12 


.12 


.12 


.12 


.11 


.11 


.11 


.11 


.10 


.10 


.10 


120 


.16 


.15 


.15 


.14 


.14 


.14 


.13 


.13 


.13 


.13 


.12 


.12 


.12 


140 


.18 


.18 


.17 


.17 


.16 


.16 


.16 


.15 


.15 


.15 


.14 


.14 


.14 


160 


.21 


.20 


.20 


.19 


.19 


.18 


.18 


.18 


.17 


.17 


.17 


.16 


.16 


180 


.23 


.23 


.22 


.22 


.21 


.21 


.20 


.20 


.19 


.19 


.18 


.18 


.18 


200 


.26 


.25 


.25 


.24 


.23 


.23 


.22 


.22 


.22 


.21 


.21 


.20 


.20 


220 


.28 


.28 


.27 


.26 


.26 


.25 


.25 


.24 


.24 


.23 


.23 


.22 


.22 


240 


.31 


.30 


.30 


.29 


.28 


.27 


.27 


.26 


.26 


.25 


.25 


.24 


.24 


260 


.34 


.33 


.32 


.31 


.30 


.30 


.29 


.29 


.28 


.27 


.27 


.26 


.26 


280 


.36 


.35 


.34 


.33 


.33 


.32 


.31 


.31 


.30 


.29 


.29 


.28 


.28 


300 


.39 


.38 


.37 


.36 


.35 


.34 


.34 


.33 


.32 


.32 


.31 


.30 


.30 


320 


.41 


.40 


.39 


.38 


.37 


.37 


.36 


.35 


.34 


.34 


.33 


.32 


.32 


340 


.44 


.43 


.42 


.41 


.40 


.39 


.38 


.37 


.36 


.36 


.35 


.34 


.34 


360 


.46 


.45 


.44 


.43 


.42 


.41 


.40 


.39 


.39 


.38 


.37 


.36 


.35 


380 


.49 


.48 


.46 


.45 


.44 


.43 


.42 


.42 


.41 


.40 


.39 


.38 


.37 


400 


.51 


.50 


.49 


.48 


.47 


.46 


.45 


.44 


.43 


.42 


.41 


.40 


.39 


420 


.54 


.53 


.51 


.50 


.49 


.48 


.47 


.46 


.45 


.44 


.43 


.42 


.41 


440 


.56 


.55 


.54 


.53 


.51 


.50 


.49 


.48 


.47 


.46 


.45 


.44 


.43 


460 


.59 


.57 


.56 


.55 


.54 


.53 


.51 


.50 


.49 


.48 


.47 


.46 


.45 


480 


.62 


.60 


.59 


.57 


.56 


.55 


.54 


.52 


.51 


.50 


.49 


.48 


.47 


500 


.64 


.62 


.61 


.60 


.58 


.57 


.56 


.55 


.53 


.52 


.51 


.50 


.49 


520 


.67 


.65 


.63 


.62 


.61 


.59 


.58 


.57 


.56 


.54 


.53 


.52 


.51 


540 


.69 


.67 


.66 


.64 


.63 


.61 


.60 


.59 


.58 


.56 


.55 


.54 


.53 


560 


.72 


.70 


.68 


.67 


.65 


.64 


.63 


.61 


.60 


.59 


.57 


.56 


.55 


580 


.74 


.72 


.71 


.69 


.67 


.66 


.65 


.63 


.62 


.61 


.59 


.58 


.57 


600 


.77 


.75 


.73 


.71 


.70 


.68 


.67 


.65 


.64 


.63 


.61 


.60 


.59 


620 


.79 


.77 


.75 


.74 


.72 


.70 


.69 


.67 


.66 


.65 


.63 


.62 


.61 


640 


.82 


.80 


.78 


.76 


.74 


.73 


.71 


.70 


.68 


.67 


.65 


.64 


.63 


660 


.84 


.82 


.80 


.78 


.77 


.75 


.73 


.72 


.70 


.69 


.68 


.66 


.65 


680 


.87 


.85 


.83 


.81 


.79 


.77 


.76 


.74 


.72 


.71 


.70 


.68 


.67 


700 


.89 


.87 


.85 


.83 


.81 


.79 


.78 


.76 


.75 


.73 


.72 


.70 


.69 



THE USE OF WEATHER INSTRUMENTS 



147 





Temperature of outdoor air in degrees Fahrenheit 


l- a 


20° 


10° 


0° 


10° 


20° 


30° 


40° 


50° 


60° 


70° 


80° 


90° 


100° 


720 


.92 


.90 


.88 


.86 


.84 


.82 


.80 


.78 


.77 


.75 


.74 


.72 


.71 


740 


.94 


.92 


.90 


.88 


.86 


.84 


.82 


.80 


.79 


.77 


.76 


.74 


.73 


760 


.97 


.95 


.92 


.90 


.88 


.86 


.84 


.82 


.81 


.79 


.78 


.76 


.75 


780 


.99 


.97 


.95 


.93 


.90 


.88 


.86 


.85 


.83 


.81 


.80 


.78 


.77 


800 


1.02 


.99 


.97 


.95 


.93 


.91 


.89 


.87 


.85 


.83 


.82 


.80 


.79 


820 


1.04 


1.02 


.99 


.97 


.95 


.93 


.91 


.89 


.87 


.85 


.84 


.82 


.80 


840 


1.07 


1.04 


1.02 


.99 


.97 


.95 


.93 


.91 


.89 


.87 


.86 


.84 


.82 


860 


1.09 


1.07 


1.04 


1.02 


.99 


.97 


.95 


.93 


.91 


.89 


.88 


.86 


.84 


880 


1.12 


1.09 


1.06 


1.04 


1.02 


1.00 


.97 


.95 


.93 


.91 


.90 


.88 


.86 


900 


1.14 


1.12 


1.09 


1.06 


1.04 


1.02 


1.00 


.97 


.95 


.94 


.92 


.90 


.88 


920 


1.17 


1.14 


1.11 


1.09 


1.06 


1.04 


1.02 


1.00 


.98 


.96 


.94 


.92 


.90 


940 


1.19 


1.16 


1.14 


1.11 


T.09 


1.06 


1.04 


1.02 


1.00 


.98 


.96 


.94 


.92 


960 


1.22 


1.19 


1.16 


1.13 


1.11 


1.08 


1.06 


1.04 


1.02 


1.00 


.98 


.96 


.94 


980 


1.24 


1.21 


1.18 


1.16 


1.13 


1.11 


1.08 


1.06 


1.04 


1.02 


1.00 


.98 


.96 


1000 


1.27 


1.24 


1.21 


1.18 


1.15 


1.13 


1.11 


1.08 


1.06 


1.04 


1.02 


1.00 


.98 


1020 


1.29 


1.26 


1.23 


1.20 


1.18 


1.15 


1.13 


1.10 


1.08 


1.06 


1.04 


1.02 


1.00 


1040 


1.32 


1.29 


1.26 


1.23 


1.20 


1.17 


1.15 


1.12 


1.10 


1.08 


1.06 


1.04 


1.02 


1060 


1.34 


1.31 


1.28 


1.25 


1.22 


1.19 


1.17 


1.15 


1.12 


1.10 


1.08 


1.06 


1.04 


1080 


1.37 


1.33 


1.30 


1.27 


1.24 


1.22 


1.19 


1.17 


1.14 


1.12 


1.10 


1.08 


1.06 


1100 


1.39 


1.36 


1.33 


1.30 


1.27 


1.24 


1.21 


1.19 


1.16 


1.14 


1.12 


1.10 


1.07 


1120 


1.42 


1.38 


1.35 


1.32 


1.29 


1.26 


1.23 


1.21 


1.18 


1.16 


1.14 


1.12 


1.09 


1140 


1.44 


1.41 


1.37 


1.34 


1.31 


1.28 


1.26 


1.23 


1.20 


1.18 


1.16 


1.14 


1.11 


1160 


1.46 


1.43 


1.40 


1.37 


1.33 


1.31 


1.28 


1.25 


1.22 


1.20 


1.18 


1.15 


1.13 


1180 


1.49 


1.45 


1.42 


1.39 


1.36 


1.33 


1.30 


1.27 


1.24 


1.22 


1.20 


1.17 


1.15 


1200 


1.51 


1.48 


1.44 


1.41 


1.38 


1.35 


1.32 


1.29 


1.27 


1.24 


1.22 


1.19 


1.17 


1220 


1.54 


1.50 


1.47 


1.43 


1.40 


1.37 


1.34 


1.31 


1.29 


1.26 


1.24 


1.21 


1.19 


1240 


1.56 


1.53 


1.49 


1.46 


1.42 


1.39 


1.36 


1.33 


1.31 


1.28 


1.26 


1.23 


1.21 


1260 


1.59 


1.55 


1.51 


1.48 


1.45 


1.42 


1.39 


1.36 


1.33 


1.30 


1.28 


1.25 


1.23 


1280 


1.61 


1.57 


1.54 


1.50 


1.47 


1.44 


1.41 


1.38 


1.35 


1.32 


1.30 


1.27 


1.25 


1300 


1.64 


1.60 


1.56 


1.53 


1.49 


1.46 


1.43 


1.40 


1.37 


1.34 


1.32 


1.29 


1.27 


1320 


1.66 


1.62 


1.58 


1.55 


1.51 


1.48 


1.45 


1.42 


1.39 


1.36 


1.34 


1.31 


1.29 


1340 


1.69 


1.65 


1.61 


1.57 


1.54 


1.50 


1.47 


1.44 


1.41 


1.38 


1.36 


1.33 


1.30 


1360 


1.71 


1.67 


1.63 


1.60 


1.56 


1.52 


1.49 


1.46 


1.43 


1.40 


1.38 


1.35 


1.32 


1380 


1.74 


1.69 


1.65 


1.62 


1.58 


1.55 


1.51 


1.48 


1.45 


1.42 


1.40 


1.37 


1.34 


1400 


1.76 


1.72 


1.68 


1.64 


1.60 


1.57 


1.54 


1.50 


1.47 


1.44 


1.42 


1.39 


1.36 


1420 


1.78 


1.74 


1.70 


1.66 


1.63 


1.59 


1.56 


1.52 


1.49 


1.46 


1.43 


1.41 


1.38 


1440 


1.81 


1.77 


1.72 


1.68 


1.65 


1.61 


1.58 


1.55 


1.51 


1.48 


1.45 


1.43 


1.40 


1460 


1.83 


1.79 


1.75 


1.71 


1.67 


1.63 


1.60 


1.56 


1.53 


1.50 


1.47 


1.45 


1.42 


1480 


1.86 


1.81 


1.77 


1.73 


1.69 


1.66 


1.62 


1.59 


1.55 


1.52 


1.49 


1.46 


1.44 


1500 


1.88 


1.84 


1.79 


1.75 


1.71 


1.68 


1.64 


1.61 


1.57 


1.54 


1.51 


1.48 


1.46 


X 





























148 



THE WEATHER 



pressure tends to crush them together as it would an empty 
bellows. But coiled springs within the shells keep them 
more or less distended. The gradual changes in atmospheric 
pressure give a slow up or down movement to the top of the set. 
This makes the pen fall or rise as it writes on the record sheet 
of the revolving cylinder. In most barographs the cylinder 
turns once round in a week, and each sheet holds a week's 
record (Fig. 106). 

157. The Measurement of Rain. — The amount of rain helps 
to determine what crops can be raised, the height of water in 
the streams for navigation and other purposes, the size of 

drains needed in city and country, 
and the kind of weather in which all 
outdoor work must be carried on. A 
record of the rainfall is useful in 
many ways. 

Rain can be caught 
ured in a home-made 
rain gage should be circular, with flat 
bottom and vertical sides. It should 
stand with its top exactly horizontal. 
It should be placed in the open away 
from trees or anything that might 
prevent rain from falling into the 
gage or cause wind eddies about the 
gage and interfere with a proper catch of rain. A common 
ruler trimmed as thin and narrow as possible may be used 
to measure the depth after each storm. The gage shown in 
Fig. 107 is better for accurate measuring of small amounts. 
The rain caught in it runs through the funnel, A, into the 
smaller can, C. It fills this can to ten times the proper 
depth. Then V10 inch on the ruler in "C" is only ^oo inch 
of actual depth of rain. In very heavy rains, some of the 
water overflows into the outer can, B, and has to be poured 
back for measuring. 




lci meas- 
gage. A 



Fig. 107. 



THE USE OF WEATHER INSTRUMENTS 149 

158. The Measurement of Snow. — Snow is harder to 
measure than rain. Unless we know how much snow falls, 
and the amount of water in it, we can not know how 
much water the soil and rivers of that region receive. 
The large outer part of the rain gage is used for snow. 
When there is but little wind the depth of snow can be 
measured in the gage, and then melted to get the depth of 
water it contains. When there is even a moderate wind with 
the storm some snow blows out of the gage. Then we need to 
measure the new snow in several places in the open yard or 
field, to find its average depth. If the average depth is 4.2 
inches, then go where it was just 4.2 inches deep, turn the 
empty snow gage bottom side up, use its top like a biscuit 
cutter to cut a "biscuit" of the new snow. Do not lift the 
gage till you slide a shingle or piece of tin across the mouth 
of the gage under the new snow. Then pick up the gage, 
carefully keeping the snow inside. Melt the snow and record 
the water as if it were rain. Record the snow as 4.2 inches. 
The most accurate method is to weigh the snow picked up in 
that way. Weather Bureau offices have weighing gages that 
show on the scale the depth of water in the snow picked up. 

The density of snow varies much in different storms. It 
may take anywhere from 7 inches to 30 inches of new snow 
to yield an inch of water. When the snow cannot be melted r 
people sometimes call ten inches of snow equal to an inch of 
water, and record it that way. 

Kansas City averages about 34 in. of rain and 25 in. of snow 
annually; while Marquette, Mich., has about 20 in. of rain and lO 1 /^ 
ft. of snowfall per year. We cannot compare records like these 
unless the snow is melted and the resulting water measured. 

159. Measuring the Temperature; Value o£ Knowing the 
Temperature. — Two places may have the same yearly average 
temperature, but one may have warm summers and cold 
winters while the other does not. Two regions may have the 



150 THE WEATHER 

same average summer temperature, but one may have much 
warmer days and cooler nights than the other. One place 
may have few and small changes in temperature, and another 
place may have many and decided changes. In one region 
alternating warm and cool periods in spring may destroy 
fruit buds, while another region with colder but more even 
temperature may be good for orcharding. All these condi- 
tions affect the crops and the industries, and the comfort and 
health of the population. For example: Corn requires hot 
days and warm nights. Grass and small grains thrive better 
in moderately cool weather. People engaged in either physi- 
cal or mental labor can do more work in a changeable tem- 
perature that becomes rather cool occasionally than they can 
where it is too warm or where the temperature is too uniform. 
A record of the temperature in every region is needed. 

In measuring air temperatures two classes of instruments 
are used: (1) Ordinary thermometers ; and (2) Self -register- 
ing maximum and minimum thermometers. Recording ther- 
mometers, or thermographs, write a continuous record of tem- 
perature, and show its changes. 

160. Ordinary Thermometers. — Thermometers usually con- 
tain mercury. The tubes, while open at the top, are filled and 
the mercury heated till it completely fills the bulb and stem. 
The tubes are then sealed. This leaves a vacuum above the 
mercury when it cools. The scale is then placed on the stem 
as described in Arts. 16 to 21 ; or the scale may be put on by 
comparing it with a standard thermometer. For very low 
temperatures, alcohol thermometers are generally used. Mer- 
cury freezes at 38.5° below zero F.; therefore, mercury 
thermometers do not record a lower temperature. 

161. Self-registering Thermometers. The Maximum. — 
In the maximum thermometer (Fig. 108) the tube is nar- 
rowed near the bulb so the mercury does not easily pass. 
The thermometer is placed nearly horizontal. When the tem- 
perature rises the mercury is forced through the narrowed 
portion {B, Fig. 108) and you can see it slipping past in small 



THE USE OF WEATHER INSTRUMENTS 151 

drops. When the temperature falls, the mercury in the tube 
remains there. Then if the bulb end be held a little lower 
than the top, so that the mercury is all joined together against 
the bulb end without crowding any back into the bulb, the top 
of the column shows the highest temperature reached since 
the instrument was last "set." To set the maximum, lower 
its bulb end to a vertical position. The mercury will then 
run past the narrowed point until the bulb is full. Sometimes 
the maximum must be jarred slightly, or whirled on its pivot, 
to make the mercury run down. After setting, the maximum 
should read practically the same as an accurate common ther- 
mometer placed beside it. The "fever" thermometer used 
by physicians is a small maximum. 




Fig. 10S. — Maximum and minimum thermometers. A marks the in- 
dex in the minimum and B the break in the mercury column of the 
maximum. 

The Minimum. — The minimum thermometer contains alco- 
hol and rests in a horizontal position. Within the alcohol in 
the tube is a small, double-headed, pin-like index (A, Fig. 108). 
Like other liquids, alcohol has a film over its surface. When 
the temperature falls and the alcohol contracts, this surface 
film draws the index back toward the bulb. When the tem- 
perature rises, the index remains still and the expanding alco- 
hol runs past it. The upper end of the index, farthest from 
the bulb, marks the lowest temperature reached since the in- 
strument was last set. To set the minimum thermometer, 
the bulb end is raised till the tube is nearly vertical. Then 
the index slides down to the "top" end of the alcohol column. 
Sometimes a slight jarring is needed to start the index. A 



152 



THE WEATHER 



minimum after setting should read practically the same as an 
accurate common thermometer beside it. 

162. Recording Thermometers. The Thermograph. — The 

thermograph (see Fig. 109) writes a continuous record of 
temperature. The thermometer bulb is a flattened brass tube 
bent into a curve and filled with alcohol. One end of this 
bulb is fastened rigidly to the frame, the other connects with 
a set of levers ending at the pen. Rising temperature ex- 
pands the alcohol and gradually straightens the curved tube ; 
this raises the pen higher. Falling temperature contracts the 



-Recording 
Thermometer. 




Fig. 109. — Thermograph. The clock turns the cylinder round once 

each week. The days and hours are marked by vertical lines; the 

degrees by horizontal lines. The pen rises and falls with all changes 
in temperature. 

alcohol and curves the bulb more; this moves the pen down- 
ward. In that way the pen writes a complete record of the 
temperature, showing all changes and the time when they 
occurred. Thermographs are used at all Weather Bureau 
stations, and are in many high school laboratories. 

163. Obtaining Accurate Temperature Records. — Ther- 
mometers should be (1) accurate and (2) sheltered and (3) 
read at proper hours. 

1. Many thermometers have errors of one or more degrees. 
They should read exactly 32° in melting ice or snow, and the 
scale should be properly spaced. It is best to compare your 
thermometer with one known to be accurate. 

2. A thermometer hanging in sunshine, or near a building, 
or over pavements or bare ground, may often give wrong 



THE USE OF WEATHER INSTRUMENTS 



153 



readings. Sunshine directly on the dark colored mercury 
warms it too much. A house wall may be too warm; or 
moisture from the house may gather on the thermometer, 













■agl §1 




SSSSs! si 




1312* 




HHU4 -— • p 








— Bjegjasjggs «~»s 








'I 




5g 


:.. . ■■ •■ ■ :- 




T '. 





Fig. 110. — Thermometer shelter; U. S. Weather Bureau Pattern. 
Maximum and minimum thermometers are shown in position. The 
ordinary rain-gage is seen at the right. 

and later be evaporated and cool the thermometer too much 
(see Ex. 10, Art. 12). Walls, pavements and bare ground re- 
flect heat. To avoid all such errors, the weather observers of 
all countries use screens or shelters for their thermometers 
(Fig. 110). The American shelter has double roof, slatted 
sides, and is placed 5 to 10 feet above sodded ground amid open 
surroundings. Its dcor opens to the north. In cities the 
shelter sometimes has to be above a flat roof ; for schools it is 
sometimes just outside a north window ; though usually neither 
of these places is as good as a shelter in the open lot. 



154 



THE WEATHER 



3. If a thermometer is read once a day, in the early morn- 
ing, the temperature record would be too low. If read only 
in early afternoon the record would be too high. Reading the 
thermometer at 7 a. m. and 7 p. m., and dividing the sum by 
2, gives a fairly correct average for the day. The Weather 
Bureau uses self-recording maximum and minimum thermom- 
eters to get the highest and lowest extremes in the 24 hours, 
then adds these extremes and divides by 2, for the average of 
the day. 1 

164. Keeping the Weather Record with Instruments. — 
The class should now use the thermometer, barometer and 
rain gage in keeping the weather record for one month. A 
home-made rain gage will do. Inexpensive thermometers may 
be compared with a reliable thermometer and used if their 
readings are corrected. Keep the record as shown in the 
above condensed and convenient form. A part of the gov- 
ernment weather records are kept in similar manner. 

















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1 If your school has a thermograph, test both those methods for a 
few days. From the thermograph 'sheet get the temperature at the 
end of each hour; add these 24 temperatures and divide by 24. This 
gives an accurate average for the day. The average obtained by the 
other methods will often differ a little from this for a single day, but 
for a month they will run about the same. 



THE ATMOSPHERE AND ITS TEMPERATURE 155 

Having learned something of the methods and the instru- 
ments by which men study the weather, let us now turn to 
some of the facts that have been learned. We begin with 
the temperature. 

III. THE ATMOSPHERE AXD ITS TEMPERATURE 
A Few Facts About the Atmosphere 

165. How the Atmosphere Is Heated and Cooled. — The 

sun's rays pass through the atmosphere to the earth without 
warming the air much. They warm the earth's surface in 
the daj^time, and the air is warmed by coming in contact with 
the warm earth, from heat reflected back by earth into the air 
and by the mixing of air as the warm air rises from the ground. 
The air is cooled chiefly by expansion as it ascends, by mixing 
with colder air, or by coming in contact with objects colder 
than itself (as with earth's surface at night), and in several 
other ways. For these reasons the air is usually warmest 
near the ground and grows colder as we ascend. (This is true 
up to 8 or 10 miles.) Recording thermometers sent up by 
kites, balloons or airplanes, have found the temperature at the 
height of 1 mile 10° or 12° colder; at 5 miles 70° to 80° 
colder; at 10 miles 120° colder; and at 20 miles about 90° 
colder that at the ground. These figures differ in different 
seasons and in different parts of the earth. There are many 
changes from day to day in the lower 2 or 3 miles of air. 

166. Unequal Heating and the Winds. — The earth's sur- 
face is heated most near the equator; also wherever there is 
most sunshine, and where the land slopes toward the sun, 
and where there is bare ground, or certain kinds of soil. This 
unequal heating is the chief cause of the winds. Warm air is 
expanded and is lighter than cold air. The warm lighter air 
is then pushed away or crowded upward by the colder heavier 
air from other places or from above. Those movements of the 
air are the winds. The greater heating at the equator is the 



156 



THE WEATHER 



principal cause of the whole system of earth's winds (See 
Arts 216 and 221). Many other influences help. 

167. The Wind and Our Personal Temperature; Why a 
Windy Day Seems Cool. — The air is usually cooler than our 
bodies, and takes away heat from the body. The wind forces 
air through the clothing and brings fresh supplies of cold air 
into contact with the body to carry away our heat. The 
harder the wind blows the faster the body loses its heat and 
the colder seems the day. 




Fig. 111. — A lath screen. These are usually arranged to roll or slide 
aside to admit sunshine. Night temperature under this screen aver- 
aged 4 degrees higher than in an unprotected orchard nearby. To left 
of center, in foreground, is seen one type of firepot used in warming the 
ground air. 

(Illustration by F. A. Carpenter, in Monthly Weatlter Review.) 

168. The Lag of Temperature; Afternoon and Night. — 

While the earth is being warmed by the sun, it is also cooling 
all the time by radiating heat out into space. During the fore- 
noon of a clear day the ground receives heat faster than it 
radiates heat, and our temperature rises. This continues 
usually till about 2 or 3 p. m. But the warmer the ground be- 
comes, the faster it radiates heat. By 2 or 3 p. m. radiation 



THE ATMOSPHERE AND ITS TEMPERATURE 157 

(cooling) usually becomes faster than the warming. At that 
moment the temperature begins to fall. Ordinarily radiation 
(cooling) continues greater through the remainder of after- 
noon and all night ; so the temperature continues to fall from 
2 or 3 p. m. until nearly morning. Then the rising sun begins 
the warming of another forenoon. 

Clouds interfere with both sunshine and radiation, and often 
make the temperature changes different. Winds that blow 
from warmer or colder regions may bring the highest or low- 




Fig. 112. — Newly planted cranberry bog. Two or three inches of 
sand were spread over the bog before the plants were set. The ditch at 
the side of the bog drains the water off quickly when danger of frost is 
passed. 

est temperature of the day at any hour of day or night, 
especially in winter. 

169. Lag of the Season. — Just as the warmest hour of day 
comes later than noon, so the warmest part of our summer 
usually comes later than June 21st, when the sun is farthest 
north ; and the coldest of our winter usually comes later than 
December 22nd, when the sun is farthest south. 

170. Night Cooling and Frost. — The cooling at night, by 
radiation, is greater on mountains and plateaus, because there 



158 THE WEATHER 

the air is thinner owing to elevation, and so permits freer 
radiation. When the cooling at night goes low enough, dew 
or frost is formed. Radiation is most rapid when the sky is 
clear, hence clear nights are coolest and most likely to have dew 
or frost. 




Fig. 113. — Frost fighting in a lemon grove. iFirepots along path near 
middle. In foreground an alarm thermometer, arranged to ring a bell in 
the watchman's headquarters when temperature falls to danger point. 
(F. A. Carpenter, in Monthly Weather Review.) 

171. Frost Protection by Checking Radiation. — Orchards, 
gardens and other crops are often protected from frost by 
using overhead screens (Fig. Ill), or fires of some fuel that 
makes dense smoke. The smoke or the overhead screens check 
radiation and sometimes keep the temperature 4° to 6° warmer 
than it would have been. 

172. Frost Protection by Warming the Ground Air. — The 






THE ATMOSPHERE AND ITS TEMPERATURE 159 

radiation that chills the night air takes place chiefly from 
the ground and vegetation. Therefore, the air cools in a 
thin layer next to the ground. Cooling makes it denser and 
heavier so that, on still nights, it remains on the ground and 
continues to cool, while the air a few feet or a few yards 
above remains warmer throughout the night. Orchardists 
often prevent frost by warming this shallow bottom layer 
of cold air with fires of oil, coal, wood, etc., placed on the 
ground, 15 to 100 per acre. 

Cranberry marshes, in Wisconsin and elsewhere, are often 
flooded with water (often completely covering the vines) 
to protect them from frost. Water holds its heat better than 
soil, and keeps the air above the water too warm for frost. 



Cold air 
remains on 
level vplaod 



aect/mvlates 
in volley 



Fig. 114. — How frosts sometimes occur both on the uplands and in 
the valley bottom, while the slopes escape. Solid arrows, cold air; 
broken arrows, warm air. 

Covering the marsh soil with an inch or two of sand also 
keeps the ground warmer and prevents some frosts (Fig. 112). 

Large orchards are often equipped with alarm thermometers 
(Fig. 113) arranged to ring a bell in the watchman's quarters 
when the temperature drops to the danger point. He can then 
leave the lighting of the fires until they are needed, and can 
tell where the fires are needed first. This saves expense. 

The Weather Bureau issues frost warnings 12 to 20 hours 
or more ahead of the cold, so that people may protect their 
orchards, gardens and crops. These warnings have saved as 
much as $100,000 in one frost in a single state. 



160 



THE WEATHER 



173. Air Drainage and Frost. — Valleys usually have frost 
later in spring and earlier in autumn than the surrounding 
slopes and low hills. On a hillside the cooled heavier air, close 
to the ground, settles downhill, leaving warmer air on the 




Fig. 115. — One type of landscape where orchards are successful on 
the slopes, while trusts prevent them both above and below. Lemon 
groves flourish beyond the rounded oak-forested hills across the lake 
near center of photograph. 

(F. A. Carpenter, in Monthly Weather Review.) 




Fig. 116. — Average date of first killing frost in autumn. 



THE ATMOSPHERE AND ITS TEMPERATURE 



161 



slopes (Fig. 114). In the valley the cold air cannot drain 
away, but keeps getting colder until frost sometimes forms. 
On the upland, radiation is faster, and the chilled air does not 
drain away much where the ground is nearly level. So both 
the uplands and the valley bottom often become colder than 
the slopes, and both have frost sometimes when the slopes do 
not. Because of this many orchards in fruit growing regions 
are placed on hillsides (Fig. 115). 

174. Wind and Frost. — The wind sometimes prevents frost 
by stirring and mixing the air. That mingles the warmer air 
above with the cold air on the ground, and sometimes keeps 
the bottom air too warm for frost. 

Notice that the frost date retreats northward in spring and 









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Fig. 117. — Average date of latest killing frost in spring. 

returns southward in autumn. The time between these frost 
dates is called the "growing season" for vegetation. About 
how many days is the average growing season in your locality ? 
In the mountainous regions of the west, frost lines are too 
irregular to chart easily (Figs. 116, 117). 



162 



THE WEATHER 



IV. THE WATER VAPOR OF THE AIR 

175. The Moisture of the Air. — Clouds, fog, rain, snow, 
dew and frost are formed from invisible water vapor in the 



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Fig. 118. — Average annual evaporation from the surface of a body, 
of water. Depth in inches; found by measurement in pans on the sur- 
face of lakes, ponds or reservoirs. 

air. This vapor is very important. From it comes the rain 
that supplies all the water in the soil and lakes and rivers of 
the earth. The water vapor in the air also affects our com- 
fort, our health and our business nearly as much as the 
temperature does. Water vapor extends above the highest 
clouds but most of it is in the lower 2 or 3 miles of air. 

176. Moisture of the Air; Its Source. — This vapor of 
water comes through evaporation, chiefly from water sur- 
faces, vegetation and the soil. (1) Evaporation from 
water surfaces ranges from a very small amount per day 



THE WATER VAPOR OF THE AIR 



163 



in polar regions, in winter, to % inch, or more, on some 
days, over tropical oceans and over 
lakes in hot dry regions (Fig. 118). 
(2) All plants give off water vapor 
through their leaves. (3) Evaporation 
from the soil varies with the kind of 
soil, the dampness of the soil, the way 
its surface has been cultivated, the dry- 
ness of the air, and the force of the wind. 
Wet soil, dry air, high temperature and 
strong winds all increase evaporation. 
Evaporation is greater from porous 
soils than from packed soils. Boiling a 
field checks evaporation. Cultivating a 
field or garden or flower bed so as to 
form a "dust mulch" an inch or so 
thick over the surface, keeps more mois- 
ture in the soil and makes the plants and 
flowers grow better in dry weather. 
("See Art. 473, How Soil Moisture may 
be conserved.") 

177. Measuring Evaporation. — You 
may find about how fast water evaporates 
in your locality in summer, by placing a 
shallow tray filled with water out of 
doors and measuring the remaining 
depth every few days. Of course you 
must measure the rainfall of every 
storm and remember that the storm 
added that much to the depth in the 
pan. Figure 118 shows the estimated 
depth that would be evaporated in a 
year from a lake or pond in different 
portions of the United States. Can you 
tell why evaporation would be so much greater in the South- 
west ? 



Fig. 119.— The sling 
psychrometer. The 
lower bulb is covered 
with muslin and is 
moistened before an 
observation. The ther- 
mometers are then 
whirled about the 
nand, and read every 
half minute or so 
till the wet ther- 
mometer ceases to 
fall lower. 



164 THE WEATHER 



PROBLEMS 



1. If an acre of clover loses 500 tons of water per season through 
the plants, and if water weighs 62.5 lbs. per cubic foot, how many 
cubic feet of water is used by the crop? An acre contains 160 sq. 
rods; how many inches deep would it be covered by that much wa- 
ter? Ans. 4.4 inches. 

2. If corn rows are 3^2 feet apart, how many rows on a strip 10 
rods wide? If the hills are 3^2 feet apart in the row, and the rows 
16 rods long, how many hills on an acre (10 by 16 rods) ? If there 
are 3 stalks in a hill, how many corn stalks on an acre? If each 
stalk gives off 250 lbs. of water in the season, how deep would the 
rainfall need to be to furnish that much water for the crop? Ans. 
14.1 inches. 

178. Evaporation Effects; Cooling. — To evaporate a quart 
of water (i.e., to change it from liquid to vapor, without 
warming the vapor any) takes about 1075 times as much heat 
as would be needed to warm the quart of water 1° Fahrenheit. 
This heat used in evaporation becomes insensible heat, which 
we cannot feel (See Art. 127, Ex. 39). All that heat is taken 
away from the surrounding air or ground or pavements or 
whatever the water was on when it evaporated. That is why 
the drying of our damp clothing makes us chilly, and why 
the sprinkling of walks or pavements on a hot day cools them 
and the air near them. 

179. Evaporation Effects; Personal Comfort. — A damjp 
day is usually more uncomfortable, in either summer or win- 
ter, than a dry day at the same temperature. (1) In winter 
out of doors, the body needs to be kept warm. Damp air 
takes away heat from the body faster .than dry air, and so 
makes us feel more chilly. (2) In hot s.ummer weather the 
body often needs to be cooled. Usually it is cooled enough by 
the evaporation of perspiration from the skin. Damp air 
evaporates less perspiration than dry air. That leaves us 
feeling warmer and more uncomfortable than when the warm 
air is dry. This is why high humidity (much moisture) in 
summer causes more suffering and heat-stroke than low hu- 



THE WATER VAPOR OF THE AIR 



165 



midity (little moisture). (3) In winter, if the air indoors 
is very dry it evaporates moisture rapidly from the skin and 
often causes a slightly chilly feeling even though the air is 
warm. If the air of our homes, schools, offices, has moisture 
enough, perspiration does not evaporate so rapidly from the 
skin, and we feel more comfortable even at a lower tempera- 
ture. It is also more healthful for lungs and throat. In 
many modern school and office buildings the heating plant is 
arranged so that humidifiers automatically throw moisture 
into the air pipes of the ventilating sys- 
tem whenever the humidity falls too low 
(see Chap. V). 

1 80. Moisture and the Industries. — 
An even or uniform humidity aids such 
work as cotton spinning ; a high humidity 
interferes with the manufacture and stor- 
age of wooden articles, food, or other 
products that might swell or spoil if they 
absorb moisure. 

181. Measuring the Water Vapor. — 
Hygrometer and Relative Humidity. — 
The amount of moisture in the air may be 
measured. One method is by using two 
thermometers, one wet and the other dry, 
arranged for whirling (Fig. 119). After 
wetting and whirling, the wet thermom- 
eter reads lower than the dry. In dry 




Fig. 120.— Hair 
hygrometer. 



summer weather it may read 15° or 
more below the dry temperature, in damp weather only a lit- 
tle lower; in foggy weather both may read alike. The dry 
temperature, the difference between the two, and a special 
table of figures, are then used to work out the per cent, of 
humidity in the air. The process is a little difficult and is 
not taken up further here. 

One form of Hygrometer, for measuring the humidity, con- 
sists of a strand of human hair with the oil removed. This 



166 



THE WEATHER 



hair lengthens with dampness and shortens with dryness. 
One end is fastened to a rigid frame, the other to the circum- 
ference of a small cylinder. A spring holds the hair tight. 
A pointer is fastened on the end of the cylinder. As the hair 
changes in length with varying humidity it turns the cylin- 
der and moves the pointer (Fig. 120). 




Fig. 121. — Frost on vege- 
tation. Frost on windows 
often shows beautiful de- 
signs. 



Fig. 122. — A photograph of dew 
and unevaporated water exuded 
from the leaf. 



182. Humidity; Dew Point. — The amount of invisible 
water vapor that can exist in the air depends chiefly on the 
temperature. Air at 74° can "hold" 1 a certain amount of 
water vapor ; if cooled to 54° it could hold only half as much ; 
at 36°, only one-fourth as much; at 20°, only one-eighth as 
much water vapor as at 74°. This fact, or law, often causes 

1 "Hold" is the most convenient word to use here, but is not strictly 
correct. Water vapor would spread through space if no air were 
present. 



THE WATER VAPOR OF THE AIR 



167 



interesting results when the temperature falls. For example, 
if air, at a temperature of 54°, is % "full" of water vapor 
(humidity 75 per cent.), and its temperature should fall to 
36°, it could not hold all of the moisture it had, and a con- 
siderable part of its vapor would be condensed into dew, fog, 
cloud or rain. The temperature degree at which this con- 
densing of vapor would begin in the cooling air, is called the 
dew point because it is the temperature at which dew, or 
cloud, fog, rain, or snow would begin to form. Just where, 
at what degree, the dew point of air is at any time, depends on 




Fig. 123. — This figure shows the general or usual relation of tem- 
perature and the dew-point throughout the day. I he dotted line shows 
about how the temperature would fall were it not for the heat of con- 
densation set free when dew forms. Note the rather sharp bend in the 
temperature curve when dew begins to form. 

the temperature of the air and the amount of moisture in it. 
All dew, frost, fog, cloud, rain, snow, etc., are formed by the 
cooling of the air below its dew point. 

183. The Forming of Dew or Frost. — As the ground and 
vegetation cool at night, by radiation, they often become colder 
than the dew point of the surrounding air. That chills the air 
resting against them and makes it colder than its dew point. 
And that in turn condenses some of the moisture in the chilled 
air into dew or frost upon the ground or vegetation. If the 
temperature is above 32°, dew is formed; if 32° or lower, frost 



168 THE WEATHER 

results. Hoar frost is made of fine crystals of ice which often 
arrange themselves in beautiful designs (Fig. 121). Dew is 
usually in small droplets. The large drops frequently seen 
on the edges of grass or leaves often come partly from the leaf 
pores of the plant. Figure 122 shows both the small droplets 
of dew, and other large drops which may have come partly 
from the leaves. 




Fig. 124. — Photograph of two cloud sheets. Taken from an airplane 
flying between the two cloud sheets. The cloud sheet below the air- 
plane is stratus clouds; the cloud sheet above the airplane is alto- 
stratus. The stratus sheet below receives the lights and the shadows 
of the upper sheet just as the surface of a body of water would. (Air- 
plane photo, Monthly Weather Reveiw.) 

184. The Forming of Ground Fog. — While dew or frost is 
forming, the air often remains clear. But the cooling may 
go far enough to chill the whole mass of air near the ground to 
below its dew point. Then part of the vapor within the 
chilled air is condensed into very small particles of water that 
remain suspended in the air as Fog. Sometimes this fog may 
be seen first in the few inches of air next the ground, gradually 
deepening as the air chills higher. 

Deep, widespread fogs are often formed by the mixing of 



THE WATER VAPOR OF THE AIR 



169 




FlG. 125. — Upper third cirrus clouds; lower half cirro-stratus. Cir- 
rus are light feathery clouds, more or less scattered. When they have 
the form of plumes with frayed or torn edges, and are moving rapidly, 
they usually indicate increasing cloudiness and rain or snow. Cirrus 
moving very slowly seldom indicate an approaching storm. In temper- 
ate zones cirrus and cirro-stratus nearly always move from a westerly 
direction. The thickening of cirrus into cirro-stratus, as shown here, 
often indicates rain or snow. The clouds seem to thicken gradually 
until the sky is hidden. This thickening is sometimes partly due to 
the growth of the clouds themselves; usually it is caused mainly by the 
coming of denser masses as the earlier clouds pass on. 









; " • 




■" 




'. -. 




■ '■ ■ .... ,,:. 
. .. .' 







Fig. 126. — Fair-weather cumulus clouds. This type of cumulus is 
often seen. Note the level bases and rounded tops. (The bases are all 
at the same height, though the distant bases appear lower because 
farther away.) These clouds do not indicate rain. 



170 



MARES TAIL 

CIRRUS 

27000 to50.000/t 



CIRRO-STRATUS 

AVERAGE 29500ft 
MACKEREL SKY 

CIRRO-CUMULUS 

10.000 to 23000ft. 



ALTOCUMULUS 

10.000 to 23000ft. 



ALTO-STRATUS 

10.000 to 23 000 ft. 



STRATO-CUMULUS 

ABOUT 6500ft. 



CUMULUS 

4500 to5000ft 



STORM CLOUD 

CUMULONIMBUS 

4500 to 24000ft. 



THE WEATHER 

TYPICAL FORMS. 



HEIGHT, COMPARISON, 
OBJECTS 



RAIN CLOUD 

NIMBUS 

3000 to 640 Oft 



STRATUS 

O to 3500 ft 




Fig. 127. — Cloud forms, in order of their elevation. 
(Note. These classes and heights should be learned.) 



THE WATER VAPOR OF THE AIR 171 

Cl-asses of Clouds. — Description 

Principal Types 

i. Cirrus. — Whitish color. Makes no shadow. Is made up of threads 
or fibers that are sometimes arranged like a feather and sometimes 
woven like cloth. Sometimes these fibers are straight; sometimes curved. 
Cirrus clouds often move very fast, but do not seem to do so because 
they are so high. They average about 5 to 7 miles above sea level. 

2. Cumulus. — The rounded heap cloud. Seen oftenest in summer. Is 
dark on shaded side and bright on sunny side. Casts a shadow on the 
ground. Cumulus range from very small to as large as a mountain. 
Their bottoms are usually flat, and may be *4 uiile to 1 mile high, while 
the tops are sometimes 3 or 4 miles higher. 

3. Stratus. — A flat, sheet-like cloud; color dark gray. It may cover 
all the sky like a blanket, or it may be broken into patches. It may 
have either clear sky or higher clouds above it. It is seen in all seasons, 
but oftenest in cool or cold weather. It is usually % to % mile high. 

Combination Types 

4. Cirro-Stratus. — Is like cirrus, only the threads are woven into a 
sheet or layer. This thin whitish sheet sometimes covers all of the sky, 
at other times only in patches or bars. Such bars are made up of 
shorter fibers than those in cirrus clouds. When cirro-stratus gets 
thicker and darker in color it sometimes becomes alto-stratus. Cirro- 
stratus clouds are about 2 to 6 miles high. 

5. Alto-Stratus (alto means high). — This is a gray sheet of high 
cloud. One type is like cirro-stratus, only thicker and dark gray in 
color; the other type is made up of small lumpy clouds joined together 
into a sheet or layer. Alto-stratus may cover all the sky or may be 
only in patches. It is 3 to 5 miles high. 

6. Cirro-Cumulus. — Balls or heaps or "fleeces" of whitish cloud. 
They are made of fibers like cirrus, and are heaped or rounded like very 
small cumulus. They cast no shadow. They are much higher than 
small cumulus, being 3 to 6 miles high. 

7. Alto-Cumulus. — A high cumulus. It is usually smaller than the 
low cumulus clouds, and looks to be rather dense or solid; 2 to 4 miles 
high. 

8. Strato-Cumulus. — Has a bottom like stratus, and tops like cumu- 
lus joined together. Dark colored underneath. Sometimes covers whole 
sky; sometimes in long rolls with gaps between. Sometimes the rolls 
are rather flat, other times they are heaped up rather high. About % 
to 3 miles high. 

9. Cumulo-Nimbus. — The thunder shower cloud. It has the cumulus 
top; is often very large. Black underneath; the tops are often a bright 
golden color on the sunny side. Tops may be 3 to 8 miles high. Rain 
falls from Cumulo-Nimbus clouds. 

10. Nimbus. — Any cloud from which rain or snow is falling. It may 
be any of the following forms: Nos. 2, 3, 5, 7, 8, or 9. 

(For illustrations of clouds, see Figs. 124 to 133.) 



172 



THE WEATHER 




Fig. 128. — Cirrus clouds. Light feathery clouds that float at an eleva- 
tion of 4 or 5 miles above the earth's surface. When in the form of 
plumes with frayed and torn edges increasing cloudiness and rain or 
snow are usually indicated, especially if the clouds are moving rapidly. 
Cirrus moving very slowly seldom indicate an approaching storm. In 
temperate latitudes cirrus nearly always move from a westerly direction. 




Fig. 129. — A cumulo-nimbus, or thunder head. This cloud has begun 
to rain, but not long ago. The longer cirrus fringe at A shows that por- 
tion probably began raining before the other visible portions. 



THE WATER VAPOR OF THE AIR 



173 




Fig. 130. — A large cumulus. Note the level base and high tops. The 
turret above each dome shows a much stronger upward current of air 
at those points. The sharp clean-cut upper edge over most of both 
domes shows that rain has not yet begun in those portions of the cloud. 
Turret "A" is slightly fringed (not very clear in cut), showing that 
rain is beginning in that part of the cloud. 




Fig. 131. — Cumulus clouds. Types frequently seen in summer. Tops 
like "A" are likely to develop showers, sometimes before long. The dark 
spot A' is the base of "A" or of a similar top behind "A." The top "B" 
is slightly fringed, showing that rain has begun. The rain at B' is 
probably falling from cloud "B." The rain at "C" apparently falls, 
from another cloud behind "A." 



174 



THE WEATHER 




Fig. 132. — Large cumulus, partly hidden. The dark clouds across its 
front are rather low clouds much nearer the camera. Note the bril- 
liantly lighted top. The sharp, clean-cut outline above shows that no 
rain has developed in the portions visible. 




Fig. 133. — Strato-cumulus, lower surface. Note the uneven shading. 
The dark spots are sometimes caused by the greater thickness of the 
cloud at those spots; sometimes by the shadows of higher clouds falling 
upon the strato-cumulus layer. 



THE WATER VAPOR OF THE AIR 175 

masses of warm air with masses of cold air ; sometimes in win- 
ter, by warm damp winds blowing over a colder region. 

185. The Forming of Clouds. — The lowest clouds and all 
the denser clouds are like fog. Clouds are formed by the con- 
densing of water vapor in the air. They are interesting and 
often beautiful. Clouds are the messengers of the air. Some- 
times they tell us of sunny days to come ; often they warn us 
of approaching storms. What they tell depends on how much 
one knows of them. 

The foregoing six pages introduce clouds and show how 
to study them for yourself. 

Figure 127 shows the principal classes of clouds, arranged 
according to their height. The accompanying table gives the 
chief divisions and a number of their combinations. Some 
cloud forms are further illustrated in Figures 124 to 133. 

In recording cloudiness in weather records, a day with %o 
or less of cloudiness is called clear; % to %o i s called partly 
cloudy; and % or more is cloudy. See Weather Record, 
page 154, and study the government's Weather Reports. 

186. Cumulus Clouds; How They Are Formed. — Clouds 
may be formed in several ways. The most important is that 




Fig. 134. — Rising air currents, due to warming of earth's surface. 
At "A" no cloud is formed. 
At "B" a small cloud results 
At "(7" a stronger current builds a much higher cloud. 

which builds the cumulus. Cumuli are formed by the cool- 
ing that takes place in ascending currents of rather warm and 
moist air. Air is warmed most next to the earth's surface 



176 THE WEATHER 

(Art. 165). Often, especially in summer, this lower air be- 
comes considerably warmer, and therefore considerably 
lighter, than the air above. Then, for a brief time, there is 
cool heavier air above, and warm lighter air below it next to 
the earth (Fig. 134). Soon this warming air below breaks up- 
ward through the overlying colder heavier air, and ascends in 
broad streams or masses here and there, while the colder 
heavier air settles downward between. The ascending streams 
of warm air continue to rise as long as they are warmer than 
the air around them at the same -height. As they rise the pres- 
sure on them becomes less. That lets them expand. The ex- 
panding cools them. Whenever the rising air cools below its 
dew point, cumulus cloud begins to form. 

187. Cumulus ; Large and Small. — The beginning of a cum- 
ulus is at the bottom of the cloud. If the rising air current at 
that height is still considerably warmer than the surrounding 
air, it will keep on rising considerably higher, forming cloud 
all the way up, and so build a tall cumulus. But if the rising 
air at the cloud base is only a little warmer tha«n the surround- 
ing air, it will rise only a little higher and so will build only 
a low-topped cumulus. The size or volume of the ascending 
air current, and the amount of water vapor in it, also makes 
a difference in the size of the cloud (Fig. 134). 

Cumuli are often fair weather clouds; at other times they 
develop into showers. By watching their growth one who is 
acquainted with clouds can usually see whether or not they 
will rain, and what paths the showers will follow. 

188. How Rain is Produced. — The fine water droplets of a 
cumulus cloud float in the air like fog. The ascending air 
currents help to keep the droplets from falling. When enough 
vapor has been condensed these droplets usually join together 
and settle downward faster than the rising air currents carry 
them upward. They then begin to fall as rain. Rain drops 
that reach the ground range from very small up to % inch 
or more in diameter. You can measure their sizes by catching 
some rain in an inch or so of flour. The rain drops will form 



THE WATER VAPOR OF THE AIR 177 

pellets in the flour. You can then put other water drops from 
a medicine dropper into the flour. Hold the dropper close 
to a ruler and carefully measure the size of the water drops 
before they fall. Then measure the flour pellets formed by 
these drops. That will show whether the pellets are larger 
or smaller than the drops that made them, and how much. 




Fig. 135. — Types of snow crystals. 
(Photographed by Mr. W. A. Bentley.) 

Then you can measure the.pellets formed by the rain, and find 
very nearly the size of the rain drops. 

189. Snow. — When the temperature in a cloud is below 
freezing, snow forms instead of rain. Snow flakes, when not 
too much broken by the wind, show many beautiful forms. 
Those in Fig. 135 were caught on a board covered with dark 



178 THE WEATHER 

cloth. The board was placed just outside a window so the 
flakes could be photographed through the glass. Many hun- 
dred different forms of snow flakes have been photographed 
by Mr. W. A. Bentley, of Jericho, Vt. 

Sleet. Either raindrops or partly melted snow flakes may fall 
through freezing air below the cloud and form pellets. If these 
pellets rattle when they strike the ground or other objects, they are 
called sleet. 

Hail.— (See Thunderstorm, Art. 194). 

Soft Hail. — Soft hail is composed entirely of snow. The pellets 
are usually small, but are sometimes a half inch or more in diameter. 

Glaze, or Ice Storm. — This is a name given to rain that falls un- 
frozen, or mostly unfrozen, but freezes as soon as it strikes the 
ground or other objects, and forms a coating of ice upon them. 
The weight of this ice sometimes causes much damage to trees and 
wires. 

V. LOCAL STORMS 

190. Showers. — The showers of summer nearly always de- 
velop from cumulus clouds. These showers sometimes form 
in an hour or two. They usually move eastward, but they 
may come from any direction. They sometimes seem to turn 
backward or sidewise, ins.tead of going forward. But you may 
learn to see beforehand when most showers are likely to de- 
velop, and what paths they will follow. 

191. Showers From the Larger Cumuli. — A cumulus cloud 
that is likely to rain nearly always builds up higher than 
others. Its bottom usually becomes blacker. Its top is bril- 
liant white or golden-white on the sunny side and dark on the 
shaded side. The top is rounded and often billowy, with a 
clean sharp edge at first that becomes fringed with wispy 
fibers as soon as rain begins to fall (Figs. 129, 131). As the 
shower develops, this fringe at the top spreads out usually 
on all sides of the cloud but much the farthest in front, be- 
cause the air current carrying the cloud moves faster above 
and brushes the fringe ahead (Fig. 137). 




LOCAL STORMS 179 

192. Showers; to Find the Paths They Will Follow. — 

All the large cumuli in the sky at a given 

time are moving in the same direction. 

Therefore, if you live at "z," in Fig. 136, 

and the large cumuli are moving from the 

southwest, clouds or showers, from "A" 

in the southwest are the only ones that 

will pass over you. Showers at "B" or 

"D" would pass by on either side (see 

also Art. 193). 

To find the direction that clouds Fig. 136.— The path 

of a cloud, 
are moving, stand so you can 

11 sight" directly past the corner of a chimney or roof 
or the top of a telephone pole, etc., to a distinct point 
on the cloud. Notice carefully the direction the cloud moves 
away from the chimney. To avoid mistakes you should stand 
so the cloud seems to move straight away from the chimney 
toward the zenith (point over your head). Then the chim- 
ney is in the direction that cloud is coming from. All this 
must be done carefully or you may make mistakes. 

193. To Foresee Showers ; the Clouds That May Rain. — 
After learning to recognize the shower clouds and to find the 
direction they are moving, the next step is to watch for the ap- 
proach of clouds that may rain in your vicinity. Generally 
those will be either : 

(a). Clouds already raining. With practice these are 
usually easy to see for some time before they arrive. 

(b). Other, growing clouds, not yet raining, that may be- 
gin to rain before they reach you. Usually these will be large 
cumuli with rather dark bottoms, and will be in one of the 
following classes : 

1. One or more separate or scattered clouds, not near another 
storm or shower. 

2. Clouds that develop near another shower. Most of these are 
in one of three classes. (See Fig. 137 and note.) 



180 



THE WEATHER 



Sometimes low stratus or strato-cumulus move in a direc- 
tion different from that of the main storm cloud. Do not 
be confused by them. Sometimes low clouds hide the upper 




Old Shower. 
Cloud 

ass 




JMi 




Fig. 137. — Growing Shower Clouds. 

In Fig. A, the growing cloud, R, is a considerable distance ahead of 
the main shower. R begins to rain on reaching you, or just before 
reaching you. That often makes it appear as though the main shower 
had suddenly jumped forward. This is a side view. 

In B, the growing cloud, S, is some distance behind the storm. 
S begins to rain on reaching you, or just before reaching you. That 
often makes it look as though the main storm had returned. Side view. 

In C, the small clouds, a, b, c, d, and the shower itself are all 
moving due eastward. The small clouds, a, b, c, d, grow rapidly 
into large clouds, A, B, C, D, and each begins to rain as it reaches 
the broken line. The shower thus spreads over all the territory east 
of the broken line, and the edge of the rain reaches you at Z. This 
is a top view. 

In D, all the clouds are moving from the southwest, and the same 
sort of spreading is shown on the north side of the storm. The rain 
spreads over all the territory east of the broken line. This is a top 
view of the storm. 

In C and D, "X" shading shows where the old shower will rain. 
"Y" shading is the added rain area from the new clouds. 

and important clouds from view. Then it is difficult to know 
what the upper clouds are doing. It is not always easy for 
a beginner to distinguish the different kinds of clouds ac- 
curately. But it is always interesting to watch showers, and 



LOCAL STOKMS 



181 



it is useful to know beforehand, as far as possible, what they 
will do. 

194. The Thunderstorm; Its Approach and Passing. — 
After a shower has become well developed, the cirro-stratus 
fringe at its top may reach many miles ahead, and is often 
the first we see of the coming storm. It is frequently more 
or less hidden by lower clouds. This high cloud, and the 









Fig. 138. — The dot is your position. The circle is your horizon. 
The double shading is the area now covered by the thunderstorm. Single 
shading is outspreading upper clouds. The arrow shows the direction 
in which the storm cloud is moving. In a and e the storm will reach 
you; b and c show how some thunderstorms pass by to one side of 
you; d and df show the narrow strips of country covered by some 
thunderstorms. These are top views. 

storm behind it, may advance broadside toward us, as in (a) 
(Fig. 138). They may pass by to one side, as in (6) or (c). 
They may travel endwise over a narrow strip of sky, as in 
(d). They may come obliquely (on a slant), as in (e). The 
high advance cloud may be thin at first, so the sun can be seen 
through it. Before long it becomes thicker and heavier. 
Later, back toward the horizon that it is coming from, you 
can see the dense black, or greenish-black, base of the storm 



182 



THE WEATHER 



cloud; then the gray, or dark blue, curtain of rain falling 
from it. Often just in front of the rain is a roll or bank 
of ragged grayish cloud that is tumbled and tossed by the 
wind. This is called the "squall cloud," and immediately 
after it usually comes the first dash of heavy rain. The rain 
may last from a few minutes to an hour or two, and may be 
steady or broken. Toward the last it usually slackens grad- 




. y mmm 



Fig. 139. — Diagram of a thunderstorm. 

A, B. Warm air flowing into and up through the cloud, largely from 
in front but often also from sides. 

D. Downward movement of air within a portion of the storm. 

Z. Cirro-stratus advance extending often far in front. 

M, N, R. Lower clouds in front of storm; almost any size and amount 
may be present. 

G. Outflowing wind of storm front. 

X. Squall cloud, a ragged roll mixing and tumbling; not always 
present. 

T. Front of main cloud. 

H, K. Points mentioned in discussing hail. 

V. Backward flow of air in rear of storm; not always present. 

ually until it stops. Not long after the rain ends, and some- 
times before it ends, the clouds begin to break. About one 
to three hours later, especially if it is toward evening, you 
can sometimes see in the east the brilliantly lighted tops of 
the departing storm cloud. The tops of cumulo-nimbus re- 
flect the light of the setting sun. 1 

i Sometimes the sun may set clear while a sheet of storm cloud 
covers most of the sky. The sun then shines under the west edge of 



LOCAL STORMS 



183 



195. The Winds of a Thunderstorm. — The winds, at the 
ground, near a thunderstorm often blow outward on all sides, 
away from the storm (Fig. 140). When a storm comes from 
the west, the wind close in front with the squall cloud, is 
from the west. When the rain is about ended the wind 
sometimes has changed to the east and is blowing back as a 
light or brisk breeze from the departing storm. When a 
thunderstorm passes near by to the north of you, you will 
often have a north wind that blows out several miles from 




Fig. 140. — Outflowing winds at the ground often occurring on all 
sides of a summer thunderstorm. Not all these winds are present with 
every storm. This is a top view of a thunderstorm area. The length 
and width of a storm may be either greater or less than shown in the 
figure. 

the storm. And when a storm passes near on the south of 
you, a similar wind often blows out from the south. If the 
storm stood still perhaps all these winds would have about 
the same force. But most thunderstorms are moving, and so 
the winds in front are usually the strongest. (Why?) The 

the storm cloud and its light is reflected from the under side of the 
cloud, giving the whole sky a brilliant pink or golden glow. A fainter 
coloring is sometimes caused in fair weather by a sheet of cirrus or 
cirro-stratus over the east or southeast sky while the sun sets clear. 
Lower clouds sometimes hide such sunsets and are lighted up by the 
reflected glow from the higher clouds. 



184 



THE WEATHER 



warm air that builds the thunder cloud and keeps it raining 
is slanting upward into the storm cloud above these outflow- 
ing ground winds, especially on the south and east sides of 
the storm. This is shown for the front side of the storm, in 
Tig. 139. 

196. The Thunderstorm; Its Lightning and Thunder. — 
Lightning is an electric flash or discharge. It is thought 
that the electricity in the cloud exists on the surface of the 

10 10 




Eig. 141. — Average annual number of thunderstorms in the 10 years 

1904-1913. 
( W. H. Alexander, in Monthly Weather Review.) 

water droplets. When many small droplets join together 
into fewer and larger drops the few large drops have much 
less surface than the many small drops had. We might per- 
haps say that this "crowds" the electricity and increases its 
intensity. When that process goes far enough an electric 
discharge takes place. This discharge is the lightning flash. 
Tall objects like trees, chimneys, spires, etc., are most likely 
to be struck, and any object much taller than its surround- 
ings should be avoided during a thunderstorm. Kite flying 
in or near a thunder storm is dangerous. 



LOCAL STORMS 185 

The lightning of a distant thunderstorm at night often 
makes a beautiful display if not hidden by other clouds. 
What is called heat lightning, is usually the reflected light- 
ning of a distant storm. 

Thunder is caused by lightning. A flash of lightning heats 
the air along its path suddenly with an intense heat. This 
causes a sudden expansion of the air. Almost instantly the 
air cools and contracts again. This sudden expanding and 
contracting of the air along the path of the flash produces 
the sound waves which we call thunder. 




Fig. 142. — The layers of hail stones. Figs. 1, 2, and 3 show the for- 
mations of hailstones having five, seven and nine layers, respectively, 
outside the central nucleus. The stippled dark portions represent snow. 

197. The Thunderstorm; Hail. — Hail is usually made up 
of alternate layers of clear ice and 01 cloudy ice or snow. 
How hail forms is not fully understood. One of the prin- 
cipal theories may be explained from Fig. 139. Suppose 
that the uprush of air in a portion of such a storm carries a 
drop of rain up into the colder part of the cloud near H, 
where the raindrop mixes with snow, freezes, then falls back 
toward K, receives a layer of water which immediately freezes 
to its icy surface ; is then carried aloft for another coating of 
snow; and so on until the stone becomes too heavy and falls 
to the ground. Hailstones may be split with a sharp knife, 
showing the layers (Fig. 142). As many as 20 to 25 lay- 
ers have sometimes been found. Damaging hail is rare in 
most places. Falls of hail 8 inches or a foot deep have been 



186 



THE WEATHER 



known. Hailstones 13 inches in circumference have been 
measured. 

198. The Tornado.— The tornado is the most violent storm 
that occurs on earth. It is something like the dust whirl- 
winds seen on street corners or in the fields, except that the 




Fig. 143. — Tornado. Rather small funnel cloud extending to ground. 




Fig. 144. — Same tornado, closer view. 



LOCAL STORMS 187 

tornado is very much larger and stronger. The tornado is 
usually not more than 50 to 500 yards wide. Some have been 
only a few yards, others a mile or more in diameter (Figs. 
143, 144 and 145). 

The rising air currents in a cumulus cloud sometimes meet 
at the proper angle to throw themselves into a whirl as they 
go up through the cloud (much as the water in a wash bowl 




Fig. 145. — Shows the base of the funnel of the same tornado when 
about one mile west-northwest of the camera. This view is from the 
side and somewhat in front, as the storm passed by. 

throws itself into a whirl as it runs down through the open- 
ing in the bottom). Occasionally this whirl in the cloud 
becomes strong enough to extend itself clear down to the 
ground, and then it is usually marked by a funnel-shaped 
or tail-like cloud. When the air whirl becomes strong enough 
this funnel cloud reaches to the ground. The stronger the 
tornado is, the wider the funnel cloud becomes. 

199. Damage Done by Tornadoes. — The damage done by 
a tornado is caused: (1) By the violent winds in the whirl, 



188 



THE WEATHER 



which blow perhaps 200 miles or more per hour; and (2) 
By the low pressure in the core of the tornado. The air in 
a tornado whirls so fast that it pulls itself away from the 
center, just as a stone pulls on the string when you whirl 
it around your head. That makes the air pressure less in 
the funnel than it is outside the funnel. The pressure of 
air is about 15 lbs. per square inch. Suppose the pressure 




Fig. 146. — Effects of a tornado, 
in the tornado center is only 10 lbs. per sq. inch, the differ- 
ence between the funnel center and outside would therefore 
be 5 lbs. per sq. inch. Then when the funnel comes suddenly 
over a closed house, the air inside the house will instantly 
push outward with a force of 5 lbs. per square inch. (How 
much would that be on one side wall of your school room?) 
That pressure is often enough to break out a wall or ''ex- 
plode" the house. We do not know just what the pressure 

Note. — The name "cyclone" belongs to a wholly different class of 
storms (see Arts. 200 and 215) and should never be used for a tor- 
nado. (1) The tornado always has the local twisting winds and a 
hanging core of revolving cloud; the cyclone never has either. (2) 
The diameter of the tornado is always a few hundred yards, or less; 
the diameter of the cyclone is always a few hundred miles or more. 



THE GENERAL STORM; A LOW PRESSURE AREA 189 

is inside a tornado, but the above is thought to be the correct 
explanation of some of the effects of a tornado. Tornadoes 
have been known to carry heavy stones high in the air; to 
carry children a mile or more and lodge them unhurt in tree 
tops ; to pluck the feathers from chickens, and to drive straws 
into boards and plank through sheets of steel. The tornado 
is confined principally to the United States east of the Rocky 
Mountains, and rarely occurs in other portions of the earth. 
Most tornadoes develop in the southeast half of a low-pressure 
area (Figs.147 to 150). 

VI. THE GENERAL STORM; A LOW PRESSURE AREA 

200. The General Storm; How It is Studied. — Thus far 
the weather may be studied by one person working alone. 
But to study the widespread storms, and to predict their com- 
ing, many countries have weather bureaus with a large num- 
ber of stations that take simultaneous observations and tele- 
graph them immediately to a central office. There the 
weather conditions at each station are written in the proper 
places on a large map. For example, the weather at Denver 
is written near Denver on the map; Chicago's weather is 
written at Chicago, etc. When the map is finished it gives 
a bird's-eye view of the weather over the entire country. 
Such a map is made twice each day, at 7 o'clock, morning 
and at 7 o'clock, evening. The forecaster can look at yester- 
day morning's map and see where the storms and the fair 
weather, and the warmer and the colder were at that time. 
Then he can look at this morning's map and see just how the 
weather conditions have traveled since yesterday. From that 
he can see about what kind of weather is coming to each state 
in the next day or two. He then writes out the weather 
forecasts for each section, and sends them by wire and by 
mail to every locality. 

You can learn to understand the weather maps, and by 
watching them from day to day you too can see the storms 



190 



THE WEATHER 




Fig. 147. — Weather map of 7 a. m. (Central Time) December 4, 1906. 
Numbers at cities give barometer reading, as 30.14 at New Orleans. 
The lines are then drawn through places having the same pressure; see 
figures at end of line. Arrows point or fly the way the wind is blow- 
ing. The crests of high pressure are over Pennslyvania, Ohio, West 
Virginia, and northern Manitoba and Saskatchewan. The principal 
center of low pressure is over western Colorado. 



THE GENERAL STORM; A LOW PRESSURE AREA 191 



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Fig. 148. — Completed weather map of 7 a. m. (Central Time) De- 
cember 4, 1906. The pressure lines (isobars) and the arrows showing 
wind direction, are the same as in the preceding chart. The broken 
lines are isotherms, showing temperature; see degrees at end of line. 
The single shading shows the cloud sheet around this Low; double 
shading shows where rain or snow has fallen in last 24 hours. Scat- 
tered cirrus clouds usually extend eastward in advance of the cloudy 




Fig. 149. — Weather map of 7 a. m. (Central Time) December 5, 1906. 



192 



THE WEATHER 



cross the country. A study of the following charts will show 
how. 

201. The Weather Map; Pressure and Winds. — Figure 
147 shows the barometer readings and the wind directions at 
a large number of Weather Bureau stations over the United 
States, at 7 a. m. Central Time, Dec. 4, 1906. The figures at 
each place give the barometer readings. Each solid line runs 




Fig. 150. — Weather map of December 6, 1906. The heavy broken 
line shows path of the Low; the small circles, its position on suc- 
cessive days. 

through places having the same pressure. That pressure is 
marked at end of the line. The barometer is lowest over 
Colorado, and highest over Ohio, Pennsylvania and Virginia 
and northern Manitoba. In paragraph 152 we learned that 
the barometer measures the weight, or pressure, of the air. 
The chart shows that on the morning of December 4th, 1906, 
the pressure was greater over Ohio than it was over the sur- 
rounding region. That greater pressure, or weight, crowded 
the winds outward away from Ohio, on all sides (the arrows 



THE GENERAL STGRM; A LOW PRESSURE AREA 193 

point or fly with the winds). The same was true over north- 
ern Manitoba. (1) The winds, at the ground, always blow 
away from high pressure. 

Over Colorado the pressure was low. It was higher on all 
sides of Colorado. That higher pressure surrounding Colo- 
rado crowded the winds towards Colorado from all sides. 
(2) The winds, at the ground, always blow (obliquely) to- 
wards low pressure. This law is shown more clearly in Figs. 
149 and 150, for December 5th and 6th, where the low is 
away from the highlands and the mountains do not interfere 
so much with the winds. 

202. The Weather Map; Clouds and Rain. — Because the 
winds are crowded toward Colorado from all sides, they can- 
not escape elsewhere and so are forced upward to higher 
elevations. As they rise they are cooled. The cooling con- 
denses some of their moisture (see par. 185) into clouds, and 
later into rain or snow. The single shading (Fig. 147) shows 
the cloud sheet already developed around this low. The 
double shading shows where rain or snow has begun. (The 
pupil should carefully review this paragraph and tell why 
rains develop around a low.) 

203. The Weather Map; Temperature. — The broken lines 
on the charts (Figs. 148, 149, 150) are called isotherms. 
Each line passes through places having the same tempera- 
ture. The degrees are marked at the ends of the lines. The 
south winds over Texas are carrying warm air northward. 
That bends the isotherms to the north a little in that section. 

204. The Weather Map ; Second Day. — In Figure 149 r 
for 7 a. m., December 5, 1906, the low has traveled to near 
Omaha. The winds blow toward the low, to the right of 
its center but curving to the left around it. The cloud and 
rain areas are larger than yesterday. The isotherms bend 
far to the north over Missouri, and far to the southward over 
the Rocky Mountains. 

205. The Weather Map; The Third Day. — In Figure 
150, the low has reached Lake Ontario. The rain-and-snow 



194 



THE WEATHEK 



area has widened still more. The winds curve towards and 
around the low. The southerly winds carry warm air far 
northward over the Alleghany Mountains. The northwest 
winds in the rear carry cold air far southward over the plains 
and Mississippi Valley. High pressure in the northwest is 
moving southeastward towards the central states. 



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Fig. 151. — Note that the storm center was near Omaha at 7 A. M. of 
the 5th ; and in Southern Ontario at 7 a.m. ( Central Time ) of the 6th. 

At Des Moines, in the path of the storm center, the wind remained 
steadily in the southeast until the storm center arrived, about 10 
a. m. of the 5th, and then changed completely around to the northwest 
in perhaps an hour or so. 

At St. Paul and St. Louis, 250 miles or so on either side of the 
storm path, the winds changed as follows: When the storm center was 
at Omaha, St. Louis wind was at arrow "a," and St. Paul wind at "A" 
or "B." When the storm center reached B (at Des Moines), St. Louis 
wind had shifted to "b" and St. Paul to about "B." 'When storm center 
had reached c, St. Louis, wind direction was "c," and St. Paul's direct- 
ion was "C." When storm center had reached d, the wind had become 
"d" at St. Louis and "D" at St. Paul. Thus, while the storm center 
passed by to north of St Louis, the wind at St. Louis shifted slowly 
from "a" to '%" "c," "d," in about 24 hours. And at St. Paul, while 
the storm center passed by on the south, St. Paul's wind shifted slowly 
from "A" to "£," "O," "D," in 24 hours. The winds always shift in a 
similar manner on each side of the path of such a general storm. 

206. Watching a Storm Go By ; Review. — By looking over 
the group of charts you will see that this storm caused cer- 
tain changes in weather at the places over which it passed. 
Those changes were not alike at all places. They are worth 



THE GENERAL STORM: A LOW PRESSURE AREA 



195 



noticing, for all well developed storms cause somewhat similar 
changes in the regions over which they travel. If we study 
these we will find many of our storms more interesting to 
watch. 

207. A Passing Storm; How the Winds Changed. — The 
center of the storm of December 4-6, 1906, passed directly 
over Des Moines. To see how the winds changed during those 
two days, both along the path of the storm center and in the 
regions on either side of the path, see Fig. 151. 



1500 



^-^iie 




Fig. 152. — Cross-section of a storm on December 5th along a line 
from Omaha to northern Xew York. The illustration shows a common 
arrangement of clouds and air movements in the lower few miles of 
air in such a storm. 

208. A Passing Storm; How the Temperature Changed. 

— The temperature at all three places rose for a day or more 
after the morning of the 4th, reaching its highest point just 
before, or about the time, the storm center arrived (midday 
of 5th) ; then began to fall again shortly after the center 
passed, reaching its lowest a day or so later. 

209. A Passing Storm; the Pressure Changes. — The 
barometer fell slowly at all three places while the storm was 
approaching ; reached its lowest reading when the center was 
nearest ; and started to rise again after the center had passed. 



196 



THE WEATHER 



The barometer fell lower and faster at points along the storm 
track than it did at places on. either side of the storm path. 

210. A Passing Storm; How the Clouds Were Arranged. 
— Cirrus clouds, from a westerly point, appeared a day or so 
ahead of this storm. Lower clouds followed; and at length 
the rain or snow. Fig. 152 shows about how the clouds of 
that storm would look if we could see a cross section of the 
storm as we can the sliced end of a layer cake that has been 




Fig. 153. — The winds of an elliptical Low. Additional arrows have 
been entered to show winds more clearly. Solid lines are barometer, 
broken lines are temperature. The center of the Low is a long line 
or trough; that makes the winds hold nearly the same direction till 
the center of the Low arrives, and then change rather quickly to 
nearly the opposite direction. 

Pressure Areas in General 

cut. The high clouds in front of a storm cannot always be 
seen, as lower clouds often hide them from view. 

The weather changes that occur with storms may be summed 
up in the following rules, which cover most of the general 
storms of autumn, winter and spring. Storms in summer are 
largely of the thunderstorm type. (See Local Storms, p. 178.) 

2ii. Summary of Changes With a Passing Storm (Cir- 
cular Law). — (1) The barometer falls as the storm center 



THE GENERAL STORM; A LOW PRESSURE AREA 



197 



approaches, and rises after the center has passed. 
(2) The winds blow from easterly or southerly points as 
the storm center approaches, and change to westerly and 
northwesterly after the center passes, (a) Along the path 
of the center, the winds remain steady till the center arrives, 
and then change quickly as the center passes, (b) South of 
the storm track the winds shift gradually from southeasterly 
through southwest to northwesterly, (c) North of the storm 




Fig. 154. — A Low in the southern hemisphere has a clockwise whirl. 
(David J. Mares in Monthly Weather Review.) 

track the winds shift gradually from easterly through north 
to northwest. The winds blow spirally towards the center, 
curving around it toward the left (in N. Hemisphere). 

(3) The air about the middle of a low is being crowded 
upward. That usually causes the development of clouds, and 
of rain or snow. 

(4) The temperature rises as the low approaches, and falls 
after the center has passed. (Remember that a rise in tem- 
perature does not always mean that a storm is coming; but 



198 THE WEATHER 

when such a storm is approaching the temperature will rise 
in its front half.) 

(5) If the low is not circular in form these changes will 
be somewhat different. 

212. Weather Changes Attending the Passing of a High 
Pressure Area. — In the same manner, the study of the highs 
in Figs. 147 and 154 shows the following rules regarding 
weather changes during the approach and passing of a high 
pressure area. 

(1) The barometer rises as a high approaches, and falls 
after the center of the high has passed. 

(2) (a) The winds in the front half of a high blow from 
points between north and west, (b) In the center of the 
high the wind is light and changeable, (c) In the rear por- 
tion of a high the winds blow from points between east and 
south. The winds blow spirally outward and away from the 
center of a high, curving somewhat to the right. The air 
in and near the center of a high is settling downward. That 
tends to evaporate clouds and clear the sky. 

(3) The temperature falls in the front portion of a high, 
and rises after the center has passed. 

Exercise 46. — Study of Passing Storms 
After learning these rules, the class should watch the daily weather 
maps, and your own local weather, daily for at least a month, to see 
how these rules apply. No two storms or high pressure areas are 
exactly alike in all respects. You must watch the weather and the 
maps a while to know how to use the rules. 

213. Lows and Highs of the Southern Hemisphere; Winds 
Curve the Other Way. — The southern hemisphere has lows 
and highs much like those of the northern hemisphere. But 
in the southern hemisphere the winds curve in the opposite 
direction (Fig. 154). At the west side of the same chart is an 
Australian high pressure area. Compare its winds with those 
of a high in the United States. 

214. Average Paths and Speed of Lows and Highs in 
the United States. — The lows and highs of the temperate 



THE GENERAL STORM; A LOW PRESSURE AREA 



199 



zones move eastward. Those of the United States pursue 
a great variety of paths. (See Figs. 156 and 157; the 
wider the paths, the more they are followed.) In Fig. 
155 the broken lines running nearly north and south show 
the average speed per day of American lows and highs. 
The actual speed of a single low or high varies from about 
1200 miles per day, down to nothing when an occasional 
storm stands still for a day or more. 













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Fig. 155. — Average paths and average daily movement of Lows and 
Highs. Heavy lines, average paths of Highs. Lighter lines, average 
paths of Lows. 

{U. 8. Weather Bureau.) 

Exercise 47. — Plotting the Paths of Highs and Lows 

Obtain the weather maps for an entire winter month, from a 
Weather Bureau station. Note the position of the center of the 
low on the first map. Take a blank map of the same kind; make 
on it a very small circle marking that position of the center of the 
low. Make a circle for the 2nd day, the 3rd, and so on. Connect 
these small circles by a line. That line shows approximately the 
path that low traveled across the country. Number the path of 
this first low "1." Mark the paths of all other lows that appear 
during the month, numbering them in the order of their coming. 

To show the paths of the highs, make a small "x" for the posi- 
tion of the center each day. Number the paths I, II, III, etc., in 
the order of their occurrence. If convenient, use a different color 
of pencil for the paths of highs. 



200 



THE WEATHER 



Often there is more than one high or low on the same day's map. 

Remember that the paths for that particular month may not be 
the average paths for that season of the year. Plot the paths for 
another month if you have time. 

The usual or prevailing paths differ with the season of the year. 

(Find how many miles per day the lows and the highs move; 
how many miles per hour. Remember that is not the speed of the 



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wind; it is the rate of progress of the whole system of winds in 
the low or the high.) 

Exercise 48. — Making a Chart of a Month's Weather 
Make a chart, like above, showing the weather of your locality 
for one month, using your class record of the weather. The weather 
observations should be made as near the same hour each day as 
possible. 

From watching the daily weather maps, and from the prep- 
aration of these exercises, it will be clear that most of our 
daily weather is controlled by the passing lows and highs. 



THE GENERAL STORM; A LOW PRESSURE AREA 



201 



215. Lows and Highs; Unusual Paths, the Cause of Un- 
usual Weather. — Whenever a period of unusually dry or 
hot or wet or cold weather occurs it is generally because the 
lows and highs have kept traveling in unusual paths. 




Fig. 156. — 1160 Lows classified, showing 27 paths. The wider the path 
the more it was followed. 



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Fig. 157. — 928 Highs classified, showing 21 paths. The wider the path 
the more it was followed. 

November, 1909, was very warm and wet over much of the 
Mississippi Valley. Note in Fig. 158 the average paths of 
lows in autumn. Fig. 159 gives the paths for November, 
1909. Notice that most of the lows in that month traveled 



202 



THE WEATHER 




Fig. 158. — Paths of Lows in an autumn month (10 years). Note the 
scattered distribution. Half the total number are near the northern 
border. Compare with Fig. 159, paths for November, 1909. 



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Fig. 159. — One cause of periods of unusual weather; paths of Lows, 
November, 1909. Most of the Lows traveled from Oklahoma or Kan- 
sas across Iowa and Wisconsin. Heavy broken line shows average path. 
The heavy rainfall, prevailing southerly winds, and warm temperature, 
thus caused over the Mississippi Valley. Shading shows rainfall, 
inches. Solid black lines, temperature above normal. Arrows show 
prevailing winds. 



GENERAL CIRCULATION OF THE ATMOSPHERE 



203 



'northeastward over Oklahoma, Iowa and Wisconsin. There- 
fore most of their rain fell where shown by the shading in 
Fig. 159. Also, while the lows were moving along those 
paths, the southerly winds in the east half of every low were 
carrying warm temperature northward over the Mississippi 
Valley. That made the month average 6° to 9° warmer than 
usual in that region, as shown by the isotherms. 




N^" 



Fig 160. — Illustrates circulation of atmosphere. Middle of pan, 
equatorial regions; ends are temperate zones. 




If Earth did nor Rotate On rotating Earth 

»-\JFPER. WITIDS — — GROUttD "WIUDS 

Fig. 161. — Principal features of the general circulation of the atmo- 
sphere. A. If the earth did not rotate, the winds would blow straight 
north or south towards the equator or away from the equator. B. As 
it is on the rotating earth. 



VII. GENERAL CIRCULATION OF THE ATMOSPHERE 

2 1 6. The General Circulation of Atmosphere. — The gen- 
eral circulation of earth's atmosphere is caused by the greater 
heat received at the equator from the sun. The heat warms 
the air most near the equator. The warm air is then lighter, 
and the colder air crowds in under it, toward the equator, 
on either side. That soon sets up movements in the whole 
atmosphere something like those shown in the water pan, 



204 



THE WEATHER 




Fig. 162. — Principal paths of Lows of the world (Approximate). 
Lows of South Temperate zone not charted. Lows in the tropics occur 
in late summer and autumn; in temperate zones, at all seasons. 




Fig. 163. — Pressure and prevailing winds of the globe for July. 
High pressure over oceans, low pressure over continents. Winds blow- 
ing inland. 

Fig. 160. In that pan the middle is the equator, and the 
ends are the poles. The bottom of the pan is straight, 
but the same movements would occur on the earth's surface. 
If the earth did not rotate on its axis, the lower winds on 
either side would blow straight towards the equator, and the 



GENERAL CIRCULATION OF THE ATMOSPHERE 205 

upper winds would blow straight away from the equator (as 
in "A," Fig. 161). But the rotation of the earth turns all 
the winds toward the right in the north hemisphere, and 
toward the left in the southern, as in "B," Fig. 161. The 
rotation of Earth is also what causes the winds of lows and 
highs to slant obliquely as we have seen (Art. 201 and Fig. 
148). The warm equator and the rotation of the earth are 
thus the chief causes of Earth's wind system. 

217. The Weather in Different Zones of the General 
Wind System. — 

(1) In the belt of equatorial calms the weather is hot 
and moist, with light variable winds and frequent heavy 
showers that are often accompanied by wind squalls. There 
are no general storms. 

(2) In the trade wind zone the winds are moderate to 
fresh, and are remarkably steady, in direction and force. 
Showers fall about the islands and along windward coasts. 
General storms occur only in late summer and early autumn. 
Those general storms are called hurricanes in the West 
Indies, cyclones in the Indian Ocean, typhoons off south- 
east Asia, and baguios in the Philippine Islands. This class 
of storm is usually 300 to 500 miles or more in diameter, with 
strong or violent winds that nearly circle about the storm 
center and blow sometimes 100 miles or more per hour. 
After traveling westward in the trade winds, the storm usu- 
ally curves out into the temperate zone and turns eastward, 
at the same time gradually becoming broader and less violent. 
West India hurricanes occasionally visit the Atlantic coast 
of the United States. Sometimes they enter the Gulf of 
Mexico and pass northward over the Mississippi or Ohio 
Valleys. Such storms damaged Galveston, Texas, in Sep- 
tember, 1900, and August, 1915, and the city of New Orleans 
in September, 1915. 

(3) The westerly air currents of the temperate zones are 
full of broad waves or surges of unequal pressure. These 
waves are the highs and lows of the weather map, which 



206 



THE WEATHER 



control the weather of the temperate zones in the ways we have 
studied. Fig. 162 shows the usual paths of the lows (storms) 
in various portions of the earth. 

218. Effects of the Sun's Annual Migration. — The yearly 
shift, or migration, of the sun north and south of the equator, 
from summer to winter, and back, affects the weather of a 
few portions of the earth in an interesting way. In summer 
the land warms more than water. That warms and expands 
the lower air most over the land. This expansion lifts the 




Fig. 164. — A summer month. Low pressure in interior. Storm tracks 
far to north. Prevailing southerly winds. Rain distributed far inland. 

upper air over the land higher than that over the oceans. 
That in turn causes some of the upper air to run off the land 
out over the ocean. This leaves less air, and therefore less 
pressure, over the land, and adds more air, and therefore more 
pressure, over the oceans. This greater pressure over the 
oceans (Fig. 163) crowds the bottom air toward the land, 
so the prevailing winds at the ground blow inland in sum- 
mer. The most notable winds of this sort are the monsoons 
of India, that carry heavy summer rains to the northern in- 
terior of that country. In the United States, the prevailing 



GENERAL CIRCULATION OF THE ATMOSPHERE 207 

south winds of summer over the Mississippi Valley are caused 
in the same way. They are of great benefit, as they carry 
moisture from the Gulf and Atlantic far northward to supply 




Fig. 165. — Pressure and prevailing winds of the globe for January. 
High pressure ot^er lands, low pressure over oceans. Winds blow sea- 
ward. 




Fig. 166. — A winter month. 

1. High pressure in interior. 

2. Storm tracks farther south and southeast. 

3. Prevailing northwesterly winds. 

4. Rain or snow distributed mostly in southeast portion. 



208 THE WEATHER 

the summer showers of the Missouri Valley (Fig. 1,64). But 
for these winds, much of the corn and wheat belt of the 
plains and north-central states would be too dry for success- 
ful farming. 

In winter, the land cools more than the ocean. That makes 
the lower air coldest over the land. This colder air fills less 
room than it did before. That lets the upper air settle down 
lowest over the land and permits upper air to run in upon it 
from over the ocean. That in turn leaves less air and lower 
pressure over the ocean and brings more air and higher pres- 
sure to the land. This higher pressure over the land (Figs. 
165 and 166) crowds the bottom air outward toward the 
oceans, in winter. That gives prevailing northwesterly winds 
and much fair cold weather to our northern plains and upper 
Mississippi Valley, during the winter months. Similar out- 
flowing winds occur on all continents in winter, except where 
other conditions may interfere. 



CHAPTER IV 
THE SEASONS— CLIMATE AND HEALTH 

I. THE SUN— THE CAUSE OF THE SEASONS 

219. The Sun's Altitude and Its Heating Effect.— The 

height of the sun above the 
horizon at noon is different for 
every different latitude upon 
any given day. It also is dif- 
ferent for any given latitude 
upon different days of the 
year. The earth receives ail 
its heat from the sun. We 
shall soon see that the nearer 
the sun is to being at the 
zenith (the point directly over- 
head), the greater is its heating 
power. Therefore, the chang- 
ing altitude of the sun is one of the principal causes of seasons 




Fig. 167. 



Exercise 49. — To Construct a Clinometer and to Measure the 
Altitude of the Sun 

(a) On a piece of cardboard about 20 in. square, mark out the 
quarter of a circle as shown in Fig. 167. To do so, make a small 
loop at the end of a piece of wrapping twine. Slip a pencil point 
through this loop. Place one finger tightly upon the string so as to 
make the radius exactly 20 in. Draw the arc of the circle from 0° 
to 90°. Next mark off the scale by dividing the distance from 0° 
to 90° into eighteen equal parts. Each space will then represent 5°. 
If the radius is exactly 20 in., the distance from 0° to 90° around 
the arc is % of 2 X 20 X 3.14 in., or 31.4 in. Each of the eighteen 
equal parts will then be a trifle less than 1% in. These 5° spaces 
may then easily be divided into five equal spaces, thus marking off 
degrees. 

209 



210 THE SEASONS— CLIMATE AND HEALTH 

(b) Tack this cardboard scale to a board about 2 ft. square. 
Drive a nail into the board at the center of the circle. Bore a 
hole in the board near its upper edge and in the center from right 
to left. Hang this instrument on the east side of the house where 
the sun can strike it at noon. 

Note. — If the instrument is to hang on the west side of the house 
make the scale by beginning with 0° in the upper left-hand corner. 
If the laboratory or school room has a south window it is most con- 
venient to mount the clinometer just inside the window. The stu- 
dents can then observe the altitude of the sun more easily and more 
frequently. 

(c) See that the clinometer hangs in a north and south line, and 
that no trees or buildings prevent the sun's striking it at noon. At 
12 o'clock one day each week, note where the shadow of the nail 
falls across the scale. Read and record with date the angle made 
by the nail's shadow with the 0° line. This angle is equal to the 
angular altitude of the sun above the horizon. Explain why. After 
making several readings, state what you have discovered. 

220. Effect of the Sun's Altitude upon Its Heating Power. 

— In all portions of the United States the sun 's rays are much 
more nearly vertical in summer than in winter. Through- 
out the United States the sun is at its highest altitude and 
its rays are most nearly vertical on June 21 ; it has its lowest 
altitude and the rays are most slanting on December 22. 
The highest and lowest altitude of the sun's rays vary with 
the latitude. At latitude 40°, which is about the latitude of 
Philadelphia, Columbus, Ohio, Springfield, 111., and Denver, 
Colo., the highest altitude of the sun is 73%° and the low- 
est, 26%°. 

Exercise 50. — To Measure the Length of Shadow When the Sun Is 
at a Known Altitude 

Place a table or desk having a level top before a south window. 
Cut out a piece of cardboard just 1 ft. square. At 12 o'clock, noon, 
on a clear day read the sun's altitude from the clinometer. Then 
set the cardboard on edge in an east-and-west line on the table before 
the window (Fig. 168). Lean the top of cardboard toward the north 
till it exactly faces the sun. The cardboard will then form an angle 
with the table top which equals 90° minus the altitude of the sun. 



THE SUN— THE CAUSE OF THE SEASONS 



211 



Its shadow now falls upon the table top. Carefully measure and re- 
cord the length of the shadow. Is the length of the shadow more or 
less than 1 ft.? How many square feet in the shadow on the table 
top? 

If the sun were not so high in the sky, would the shadow then be 
longer or shorter than you find it to be? Would the area of the 
shadow be greater or less? 

If the sun were higher in the sky, what would then be true? 

How does the altitude of the sun affect the length and area of the 
shadow? 

Do you see that if it were not for the cardboard 1 ft. square, or 
1 sq. ft. in area, the sun's rays would fall upon that portion of the 
table top which is covered by the shadow? 

"Would the energy in 1 sq. ft. of sun's rays fall upon a larger or 
smaller area of table top if the sun were at a lower altitude? 

What would be true if the sun were at a higher altitude? 

When 1 sq. ft. of the sun's rays is spread over a large area, is that 
area heated more or less than when the rays are spread over a small 
area? 




Fig. 168. — Measuring the board's shadow on December 22, at latitude 

40°, North. 

22i. How the Sun's Heating Power Changes with Sea- 
sons and Latitude. — Since, at latitude 40°, the highest alti- 
tude of the sun is 73%° and its lowest altitude is 26% °, it 
is easy to show the area of the earth's surface over which 1 
sq. ft. of sun's energy is distributed at the summer solstice 
and at the winter solstice. In Fig. 169 the horizontal line 
represents the earth's surface. Two parallel lines, 1 cen- 
timeter apart, and cutting the horizontal line at an angle of 
731/2°, are drawn to represent the sun's rays June 21 and the 
two parallel lines also 1 centimeter apart, but cutting the hori- 



212 



THE SEASONS— CLIMATE AND HEALTH 




zontal line at an angle of 26%° represent the sun's rays 
December 22. It is evident from this figure that the sq. ft. 
of sun's rays is spread over just about twice as large an 
amount of earth's surface on December 22 as on June 21. It 

follows that the sun will heat 
the earth's surface but one-half 
as much on December 22 as it 
will on June 21. 

In a like manner Fig. 170 
shows how the area of earth's 
surface upon which 1 sq. ft. of 
sun's energy falls varies at lati- 
tude 49°, the north boundary 
line of the United States. On 
June 21, the altitude of the sun at noon at 49° north latitude 
is 64y 2 °; on December 22, it is but 17%°. In Fig. 170 the 
two parallel lines are therefore drawn at angles of 64%° 
and 17y 2 ° to the horizontal. By measuring the distances 
between the two pairs of parallel lines it is seen that the 1 
sq. ft, of sun's energy is spread over about three times as 
much of the earth's surface on December 22 as on June 21. 



Fig. 169. — Slant of sun's 
rays at 40° latitude, June 21 
and December 22. 





Fig. 170. — Slant of sun's rays at 
latitude 49° on June 21 and Decem- 
ber 22. 



Fig. 171. — Slant of sun's rays 
at latitude 30° on June 21 and 
December 22. 



Therefore, at north boundary of the United States the sun 
leats the earth's surface but about % as much at noon on 
December 22 as it does at noon on June 21. 

In the same way Fig. 171 shows how the heating power of 



THE SUN— THE CAUSE OF THE SEASONS 



213 



the sun varies at latitude 30°, approximately the south bound- 
ary of the United States. The altitude of the sun at noon, 
at 30° north latitude on June 21 is 83y 2 °, and at noon on 
December 22, it is 36y 2 °. It is seen from the figure that the 
sun's rays spread over about 1% times as large an area of 
earth's surface in the winter solstice as at the summer solstice. 
From these facts would you expect the greater difference in 
temperature between summer and winter in North Dakota or 
in Texas? 




Fig. 172.— The length of day. 

222. Length of Day and Its Effect upon the Heating 
Power of the Sun. — The days and nights are always equal 
in length at the equator, 12 hours each. The poles of the earth 
have six months day and six months night. Between the 
equator and the poles, the length of day and night is con- 
stantly changing. At latitude 40° north, the days vary in 
length from about nine hours on December 22 to 15 hours 
on June 21. The farther north we go the longer the summer 
day becomes till we reach the north pole when the day is 
six months in length. Just why this is so is easily shown 
by experiment. 



Exercise 51.- 



-To Show Why the Length of Day Varies at Different 
Places on the Earth's Surface 



(a) Use an orange or a small schoolroom globe for this experi- 
ment, and perform it in the evening or in a darkened room. Place 



214 



THE SEASONS— CLIMATE AND HEALTH 



a lighted lamp upon the table and hold the orange a few feet from 
it. If you use an orange, let the stem and the bloom scars of the 
orange be the two poles and draw a line about the orange to represent 
the equator. Let the north pole be tilted toward the lamp 23^°. 
Now note as carefully as possible the position of the dividing line 
between the lighted and unlighted surfaces of the sphere. Draw a 
pencil line around the sphere to mark this line. If we now mark 
the 40th parallel of latitude on the sphere, we shall find that about 
1 %4 of it was lighted. This means that, if we rotate the sphere 
upon its axis, that any point upon the 40th parallel would be in 
the light during 1 %4 of a rotation. Therefore, the day at the 40th 
parallel is 15 hours in length on June 21, or at the summer solstice. 
At this same time the pole is constantly in the light, and just % of 
the equator is lighted. 



zenith 




8eta 7.30 P.M. 



Sun Sets 4.30^" 

Fig. 173. — Showing the different positions of the sun at sunrise, at 
noon, and at sunset on June 21 and on December 22, at 40°, north 
latitude. 



(b) Repeat the exercise with the north pole tilted 23^2° away 
from the light. We then find that but %4 of the 40th parallel is 
lighted; that the north pole is without light; and that the equator 
is again exactly half lighted (Fig. 172). 

This increased length of day greatly increases the sun's 



THE SUN— THE CAUSE OF THE SEASONS 215 

power of heating the earth's surface and the atmosphere in 
the north latitudes during our summer months. 

1. Notwithstanding the fact that the vertical rays of the 
sun never fall farther north than the Tropic of Cancer, 23 y 2 ° 
north latitude, it still is true that for three months from May 
5 to August 5 the zone t of the sun's greatest heating is about 
41° north latitude. 

2. During the 45 days from May 31 to July 16, the region 
about the north pole actually receives more heat than does an 
equal area at any other portion of the earth's surface. 

3. And again, it can be shown that, at the time of the 
summer solstice, the region of the north pole is receiving 36 
per cent, more heat than an equal area at the equator is then 
receiving during the 2^-hour day. 

If these are facts, why does not the north polar region be- 
come warmer? 1. Because the north pole receives no heat 
whatever from the sun for six months each year. 2. Because 
nearly all of the heat furnished by the sun during the sum- 
mer months is consumed in melting the ice and snow formed 
during the long winter months. During the following winter 
a fresh supply of ice and snow again accumulate in the polar 
regions. 

Without a knowledge of these facts it is impossible to un- 
derstand the seasonal changes of the weather of the United 
States. 

The maximum temperature of a summer day in the United 
States rarely occurs in the southern states; it most frequently 
occurs in the region extending from Oklahoma and Illinois to 
South Dakota and Eastern Montana. Can you explain why 
this should be so ? 

Indian corn (maize) requires high temperature both day 
and night during about three months, or its growing season. 
Can you give some reasons why Illinois and Iowa are the 
greatest corn-producing states of the Union (Fig. 173). 

223. Summary. — There are two chief causes of our sum- 



216 THE SEASONS— CLIMATE AND HEALTH 

mer and winter seasons in the United States: (1) The change 
in the altitude of the sun and the consequent change in its 
heating power; (2) the great difference in the length of day. 
Both of these are, of course, caused by the tipping of the 
earth's axis 23%° from the perpendicular to the plane of the 
earth 's orbit, and the earth 's revolution about the sun. Since 
these facts are studied in geography further study of them 
is omitted here. 

II. CLIMATE AND LIFE 

224. Meaning of "Climate" and "Weather."— By 

weather, we mean the condition of the atmosphere at some 
particular time and at some particular place. The weather 
at Chicago frequently differs considerably from that at Buf- 
falo or Albany upon any particular date, but the climate of 
these cities is quite similar. In speaking of the weather we 
refer to the temperature, the percentage of sunshine or cloudi- 
ness, the wind, and the precipitation upon a particular date. 
By climate, we mean the average atmospheric conditions 
existing in a certain locality for a period of time, especially 
as they affect the animal and plant life of the region and the 
health and comfort of the inhabitants. When considering the 
climate of any region in reference to health we note: 

1. The average temperature and the changes in temperature. 

2. The average relative humidity and the changes in humidity. 

3. The prevailing direction and strength of the winds and how 
they vary. 

4. The average relative amounts of sunshine and cloudiness. 

5. The average rainfall for the year and the particular seasons 
at which it is heaviest and lightest. 

6. The prevalence of fogs and of dust and smoke in the air. 

7. The altitude of the region and the consequent density of the air. 

All these factors taken together determine, in a large meas- 
ure, the plant and animal life of the region and the health and 
comfort of the inhabitants. 

225. Plant Life Determined by Climate. — So completely 



CLIMATE AND LIFE 



217 



does the climate of any region control plant life, that it is 
usually with considerable difficulty that man is able to grow 
plants in any other than their native land or one having a 
similar climate. The character of the soil has, of course, con- 
siderable influence in determining plant life, but climate is 
the chief factor. The trained botanist can tell, practically, 
the climate of a certain region by observing the native flora, 
or plant life, of that region. As the climate of a certain re- 
gion changes, the flora of that region also changes. In ages 




Ml* 97* 





Sff*. 




Fig. 174. — Average annual rainfall map of the United States. 

past, during the Glacial Period, most of central North America 
north of the 40th parallel of latitude, was covered with ice. 
The climate then must have been similar to that of the arctic 
zone today. The flora, or plant life, which developed as the 
ice sheet retreated must have been similar to that now existing 
in British America near the arctic circle. In certain moist, 
cool canyons as far south as Illinois and Kentucky, specimens 
of this northern flora still linger, while the flora of the rest 
of the region long ago changed to that typical of the temperate 
zone. 



218 THE SEASONS— CLIMATE AND HEALTH 

While it is true that plants may survive when transplanted 
to a region having a climate somewhat different from that of 
their native haunts, they do not thrive ; they develop only as 
dwarf and inferior specimens. The cactus and yucca, natives 
of our arid western plains, often survive when transplanted 
to the fertile plains of the Mississippi valley, but they little 
resemble the sturdy specimens growing in their native climate. 

To the extent that man is able to control and modify the 
climate of a given region, he can raise successfully plants of 
almost any species anywhere on the face of the earth. In 
the green houses and conservatories of the temperate zone, 
tropical vegetation grows with luxuriance in the dead of win- 
ter. "When irrigation is applied to our western plains, they 
blossom forth with all the productiveness of the most favored 
regions of the earth ; yet, all that man has done is to devise a 
plan for supplying the moisture to take the place of the rain- 
fall which is insufficient (Fig. 174, Rainfall Map). 

226. Animal Life Dependent upon Climate. — Animal life 
is also largely dependent upon climatic conditions. The 
higher forms of animal life, however, show greater power of 
adaptation to changed climatic conditions than do the forms 
of plant life. While it is true that the polar bear of the 
arctics and the monkey and the parrot of the tropics live side 
by side in the zoological gardens of the temperate zone, it is 
not from choice, nor are they healthy, vigorous, happy, or 
comfortable while doing so. In a large measure man must 
provide a modified climate in order to save their lives. To 
the extent that either plants or animals become adapted to 
changed climatic conditions, we say that they have become 

ACCLIMATIZED. 

227. Man's Relation to Climate. — By nature, man is one of 
the hardiest of animals. His power of endurance equals, if, 
in fact, it does not exceed, that of any other form of animal 
life. A lone man on foot has been known to run down and 
tire out the wild horse and the wild turkey. From choice, 
man dwells contentedly in almost every climate on the face of 



THE FACTORS WHICH DETERMINE CLIMATE 219 

the earth. He even delves into the bowels of the earth and 
soars aloft among the clouds. He survives extreme exposure 
and retains his health, strength, and bodily vigor while en- 
gaged at the hardest labor for many hours each day. As long 
as he labors out of doors in the fresh air and in the sunshine, 
receives an abundance of nourishment) and sleeps eight hours 
each night in the open air, he outstrips nearly every other 
type of animal life in health, bodily vigor, and power of 
endurance. 

Usually, it is when man violates one or more of these condi- 
tions that he becomes a puny, delicate creature, an easy prey 
for disease. The experience of every polar expedition in 
history is positive evidence of the truth of this statement. 
Pioneer life, with all its exposure and privations, has always 
developed a people of exceptional vigor and hardiness. 

It is almost wholly man 's unwise and unintelligent attempts 
to protect himself against the inclemency of weather and cli- 
mate which have produced conditions favorable to the trans- 
mission of disease from one person to another and at the same 
time have so weakened his bodily resistance that he easily 
succumbs to almost any disease.. Among all classes, from the 
wealthy to the very poor, two other causes of ill health are 
evident : ( 1 ) Lack of sufficient and suitable nourishment ; and 
(2) lack of proper amount of sleep and rest. The wealthy 
suffer from these causes because of self-indulgence, the poor 
suffer because of their poverty. 

III. THE FACTORS WHICH DETERMINE CLIMATE 
A. Temperature 
228. Seasonal Changes in Temperature. — 

Exercise 52. — Study of the Average Temperature Maps of United 
States for July and January (Figs. 175 and 176). 

What and where is the highest average temperature for July? 
What and where is the lowest average temperature for July? 
What and where is the highest average temperature for January? 
What and where is the lowest average temperature for January? 



220 



THE SEASONS— CLIMATE AND HEALTH 



In which month, then, July or January, is found the widest differ- 
ence of temperature within the boundaries of the United States? 

Review the study of the effects of the sun's altitude and length of 
day upon the temperature (Arts. 220 and 222) and explain why 
January should cause a wider range of temperature than does July. 

Does New Orleans, La., or Grand Forks, N. D., have the greater 
variation in temperature between summer and winter? Why should 
this be so? 

Why should the 70° isotherm bend so far south during July in 
Colorado and New Mexico? Trace the 70° isotherm throughout its 




Fig. 175. — Average temperature for July, 25 years. 

length explaining all the bends in it. Remember that the principal 
factors in determining temperature are: (1) Altitude of the sun; 
(2) length of day; (3) prevailing wind direction; (4) proximity to 
bodies of water; (5) presence of mountain ranges. 

What portions of the United States are so situated that the cli- 
mate, especially the temperature, is largely determined by the ocean? 
(Recall the most frequent paths of lows and highs across the 
United States.) Account in part, at least, for the temperature along 
the coast of California? 

After studying the July and the January maps, state whether the 



THE FACTORS WHICH DETERMINE CLIMATE 



221 



Atlantic or the Pacific Ocean has the greater effect upon the nearby 
portions of the United States. Why should this be so? 

In studying such maps as these, we must learn to estimate the 
temperature of any locality on the map. Chicago, for instance, has 
an average temperature for July of about 71° or 72° ; St. Louis, of 
about 76° or 77° ; New Orleans, of about 82°. For January, Chi- 
cago has an average temperature of about 22°; St. Louis, of about 
29°; and New Orleans, of about 52°. 

About what average temperature has Boston for July? New 
York City? Baltimore? Charleston, S. C? New Orleans? Santa 
Fe, N. Mex.? San Francisco? Denver? Bismarck, N. D.? St. 
Paul, Minn.? Portland, Oregon? 

Estimate the average temperature of each of these places for 
January. 



te3: 




Fig. 176. — Average temperature for January, 25 years. 



B. Winds 

229. Wind, Another Important Element of Climate.— The 
temperature and humidity may be the same for two different 
localities. But if one be a sheltered place where wind veloci- 
ties are low while the other be exposed to high wind velocities, 



222 



THE SEASONS— CLIMATE AND HEALTH 



we know from experience that the exposed place seems to be 
much the colder and more uncomfortable in winter and much 
the cooler and more comfortable in summer (Art. 167). Pro- 
tection against the chilling effect of the wind in winter is nec- 
essary. The clothing we wear, the wool, the fur and the hair 
of animals, and the feathers of birds, all serve as a protection 
against the chilling wind by retaining a layer or envelope of 
warm air next to the body. High winds disturb this layer of 
warm air, thus cooling the body. 




Fig. 177. — Average wind velocity, miles per hour. Shaded areas, 
above 10 miles per hour. 

230. Wind Velocities in the United States. — The Weather 
Bureau records for years past give fairly satisfactory infor- 
mation regarding tfce wind velocities. The principal facts 
of wind velocity over the United States are easily shown (Fig. 
177). From this map we see that the highest average wind 
velocities, i.e., 10 miles per hour or more, are along the coasts, 
over the Great Plains Region east of the Rocky Mountains, 
and in the region of the Great Lakes. 



THE FACTORS WHICH DETERMINE CLIMATE 223 




Fig. 178. — Sunshine average for 15 years, June, July, and August. 




Fig. 179. — Sunshine average for 15 years, December, January, and 

February. 



224 THE SEASONS— CLIMATE AND HEALTH 

The records of the Weather Bureau also show these facts: 

1. The lowest average wind velocities are found in the valleys of 
the interior. 

2. The greatest wind velocities are found to occur in the months of 
March and April, while the lowest velocities occur in the months of 
July and August. 

3. All high altitudes have a tendency toward high winds, the 
sharper the point, the higher the winds. 

4. In general the west slope of mountain ranges has a higher aver- 
age wind velocity than the east slope. 

How do you explain each of these facts ? 

There are really two regions of relatively high winds in the 
interior of the United States: (1) The Lake Region, and (2) 
the region of the Plain States. The high winds of the Lake 
Region are to be accounted for, first, because this region lies in 
the path of the numerous northwest storms, and second, be- 
cause the water surfaces offer less resistance to the moving air. 

The high winds of the western plains may also be accounted 
for, first, by noting the even slope of the land from the Rockies 
eastward and the treeless character of this region, and second, 
the marked difference in the temperature of the mountain 
region on the west and of the Mississippi valley on the east 
during the summer months (see Fig. 177). 

As an aid in selecting a location having a suitable climate 
little general information regarding winds can be given. 
Both their velocity and direction are largely determined by 
local conditions. 

C. Sunshine 

231. Sunshine. — Physicians, as well as all thinking and 
observing people, have great faith in the curative and health- 
giving power of sunshine. The sun bath is frequently pre- 
scribed in the treatment of many diseases. Direct sunlight 
is known to be one of the best of germicides ; most disease germs 
die quickly when exposed to the direct rays of the sun. Even 
diffused sunlight is known to have great germicidal effects. 
So widespread and strong has become the faith in the beneficial 



THE FACTORS WHICH DETERMINE CLIMATE 225 

effects of sunlight, that modern architecture has felt its in- 
fluence. Modern dwellings as well as hospitals and sana- 
toriums are being constructed more and more with the view 
of admitting the largest amount of direct sunlight possible. 
Figs. 178 and 179 show the relative amounts of sunshine for 
the United States for the summer months and the winter 
months. 

Exercise 53. — Study of the Sunshine Maps, Figs. 178 and 179. 

What portion of the United States has the highest percentage of 
sunshine? What portion the lowest? 

Is the percentage of sunshine greater in the summer or in the win- 
ter? 

232. The Ideal Climate. — There is no such thing as a cli- 
mate which is ideal for all people or for any person every 
month in the year. A climate which exactly suits one person 
may be unacceptable to another. Many people are well 
pleased with the climate of southern California near the coast 
What are the characteristics of that climate, as regards: (1) 
Temperature, summer and winter; (2) annual rainfall; (3) 
sunshine, summer and winter; (4) altitude; (5) wind 
velocity; (6) evaporation? 

For many years northeastern New Mexico has been regarded 
as the center of a very favorable region for the treatment of 
tubercular patients. What are the characteristics of that re- 
gion? 

233. Seeking Health in a Change of Climate. — Just as 
Ponce de Leon and other adventurers of the 15th and 16th 
Centuries were journeying over the earth in search of the 
"fountain of youth," so thousands of people are now con- 
stantly on the move in search of a climate which insures them 
better health. They spend their winters in southern Califor- 
nia or Florida and their summers in the Adirondacks or on the 
northern lakes and are ever seeking renewed health. Some- 
times these changes of climate are made at the advice of the 
physician. Probably many experience beneficial effects from 



226 



THE SEASONS— CLIMATE AND HEALTH 



such changes of climate and occupation. However, some 
questions may well be asked: Do the beneficial effects result 
entirely from the change in climate? Was that the only cli- 
mate which would have benefited the patient ? To what extent 
do other elements, such as change of occupation, rest from la- 
bor, change in habits, change in companions, and freedom from 
responsibility, enter as factors? Those who have given the 
largest amount of thought to this matter and who are best able 
to judge agree that these are difficult questions to answer. 







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Fig. 180. — Climatic regions of the United States. 



IV. CLIMATIC REGIONS OF THE UNITED STATES 

234. Climatic Areas. — The area of the United States pre- 
sents nearly every variety of climate to be found in the tem- 
perate zone. The United States may be divided roughly into 
nine fairly well-defined climatic areas. But within each of 
those areas there is considerable variation due to local causes. 
Altitude largely affects temperature and wind. Nature of the 



CLIMATIC REGIONS OF THE UNITED STATES 227 

earth 's surface largely determines wind velocity and direction 
and often rainfall. The proximity of cities, forests, and bodies 
of water largely determines the purity of the air, the presence 
of dust and smoke, the prevalence of fogs and of local winds 
(Fig. 180). 

235. First Region. — The first region comprises southern 
Wisconsin, much of Iowa and Illinois, Indiana, Ohio, the 
Lower Peninsula of Michigan, Pennsylvania, New York, and 
New England. This region has an average temperature for 
July of 70° to 75° and for January of 20° to 30°. It has a 
summer humidity of about 70 per cent, and a winter humidity 
of about 80 per cent. It has about 60 per cent, of sunshine 
in the summer and 40 per cent, in winter. Its wind veloc- 
ities range from moderate to high. It lies in the path- 
way of a large majority of the storms which pass across the 
United States and therefore is subject to sudden and severe 
changes of weather. Its average rainfall is about 40 in. In 
this territory live about 45,000,000 people, nearly one-half of 
the population of the United States. Here is found also more 
than one-half of the wealth and influence of the nation. With 
the exception of the Adirondacks, the White Mountains, north- 
ern Maine, and the lake shores of northern Michigan, this re- 
gion is seldom frequented by the seekers after health. 

236. Second Region. — This is the Gulf States Region, with 
its comfortable winter temperature and high humidity and its 
rather high percentage of sunshine. Portions of it are used as 
a winter resort by those who do not wish to face the rigor of a 
northern winter. The summer climate of the Gulf Region 
is unpleasant. Its high average temperature, high humidity 
and nearly 60 in. of rainfall are neither pleasant nor invigorat- 
ing. Nevertheless, the higher altitudes of the mountainous 
regions of western North Carolina and Virginia receive high 
praise as health resorts. 

237. Third Region. — This is the great semi-arid region of 
the southwest, including western Texas, New Mexico, Arizona, 
southern Utah, Nevada, and southeastern California. High 



228 THE SEASONS— CLIMATE AND HEALTH 

temperatures, high evaporation, high percentage of sunshine, 
low rainfall and low humidity characterize this region. For 
many years this region has been highly recommended for con- 
sumptives. Most of this region has the "throb and glow of 
the tropics." 

238. Fourth Region. — Southwestern California has a cli- 
mate of perpetual warmth, much sunshine, soft humid air with 
moderate rainfall. Dr. "Woods Hutchinson says, "This re- 
gion escapes the bane of the tropics, steaming days and swel- 
tering nights, by virtue of the snow-capped mountains on the 
one hand and the cool blue sweep of the Kuro-Siwo, or Japan 
Current, on the other. Southern California has the sun elec- 
tricity of the tropics, with the cool nights of the green rain 
belt, the fire of the South with the stamina of the North. The 
blue sea, bright sunshine and white mountains that made the 
glory that was Greece and the grandeur that was Rome, are 
also hers. She will some day be the Greece of the New 
World." 

239. Fifth Region. — The Northwest Coast, comprising 
Washington, Oregon, some of Idaho and northern California, 
has a summer climate as delightful as the winter climate of 
southern California. The temperature is. relatively even and 
moderate while during the winter season the humidity and 
rainfall are high and the percentage of sunshine correspond- 
ingly low. 

240. Sixth Region. — This is the mountain climate of the 
United States, the climate of the "backbone" of the continent. 
In many respects this is a region of unsurpassed climate for 
those who wish life, vigor, and energy. It is characterized by 
moderate severity in winter and a pleasant warmth in summer. 
Its humidity ranges from 50 to 60 per cent, the year around. 
It has a high percentage of sunshine both summer and winter, 
and plenty of pure, relatively dry, crisp air, free from dust 
and fogs. 

241. Seventh Region. — The Dakotas, Minnesota, and north- 
ern Wisconsin comprise most of this region. Lying as it does 



PEOTECTION AGAINST UNFAVORABLE CLIMATE 229 

in the path of storms, this is a region of sudden and severe 
weather changes. Its winters are severe; its summers are 
fairly moderate but with high temperatures frequently during 
the middle of the day. The relative humidity of the eastern 
portion of this region is rather high the year around. 

242. Eighth Region. — The eighth region comprises Ne- 
braska, Kansas, Oklahoma, and northern Texas. It is char- 
acterized by high winds, low amount of rainfall, fluctuating 
temperature, rather low humidity, and high percentage of sun- 
shine. It has the most characteristically continental climate 
of any region of the United States. 

243. Ninth Region. — This region has some of the character- 
istics of the Eighth Region but has lower wind velocities and 
higher amount of precipitation. Its average temperature is 
fairly moderate, being affected in portions by the higher alti- 
tudes of the Appalachian Mountains. Its humidity is con- 
siderably lower than that of either the First Region or the 
Second Region between which it lies. It has an average sum- 
mer temperature of 75° to 80° and an average winter tempera- 
ture of 30° or 40°. The amount of rainfall is ample, about 
40 or 50 in. 

V. PROTECTION AGAINST UNFAVORABLE CLIMATE 

244. Accepting a Climate.— Whether it is best so or not, the 
fact remains that it is impossible for most of us to choose the 
climate in which we would live. Most of us are obliged to 
spend all the year, if not all our lifetime, in the climate where 
we find our place of labor. Even were we convinced that a 
certain climate, southern California for instance, is the most 
favorable for our health and comfort, it is evident that we can 
not all take up our abode there. The First Region with its 
extreme climatic changes will never again, within the lifetime 
of anyone now living, be less densely populated than it is 
today. On the contrary the population of that region will 
doubtless double and redouble in the next quarter- and half- 



230 THE SEASONS— CLIMATE AND HEALTH 

century. The real question, then, is not whether the climate 
of this or any other region is the most healthful to be found. 
The real question concerning a climate is whether it is rea- 
sonably healthful. As a second question we should ask, Is it 
possible so to live, so to condition our surroundings, that we 
may be strong and healthy even in a region having an un- 
pleasant climate ? 

245. Problem of Indoor Climate. — Only in recent years has 
the problem of protecting ourselves against severe climatic 
conditions received close attention. Most people, even now, 
give little or no attention to any element of indoor climate 
other than temperature. They make no special provision for 
fresh air and but little provision for direct sunshine in their 
rooms; they pay no attention to the humidity of the air in 
which they live. In the winter they shut themselves up in 
stuffy, nearly air-tight, often sunless, draught-stricken, over- 
heated, dust-laden rooms. Their only thought is to maintain 
a temperature of 70° or more. The highest and best authori- 
ties say that about one-half of all deaths are the result of pre- 
ventable diseases, and that a more intelligent and rational plan 
of protecting ourselves against the inclemency of climate and 
weather would materially decrease sickness and death from 
these causes. Those among us who disregard the laws of san- 
itation find their powers of resistance so weakened, their vital- 
ity so lessened, that they are easily attacked by colds, influenza, 
tuberculosis, pneumonia, and other diseases. And they, in 
turn, spread these diseases among all with whom they come in 
contact. 

246. The Ideal Indoor Climate or Air Condition. — We all 
know how delightful and pleasant is the soft balmy air of 
spring and early summer. We know how we long to be out 
of doors in the sunshine on a spring day and what renewed 
life and vigor such conditions give us. The ideal conditions 
for indoor air are those which closely resemole outdoor air of 
spring or early summer. These conditions are : a gentle breeze, 
a flood of health-giving sunlight, a humidity of 50 or 70 per 



PROTECTION AGAINST UNFAVORABLE CLIMATE 



231 



cent., air nearly free from dust, and, lastly, a temperature 
which varies with the occupation, clothing, habits, and age of 
the individual. We cannot completely control the amount of 
sunlight, but we can so construct our houses that we may en- 
joy all the sunshine there is ; the other conditions we can usu- 
ally secure without great cost or effort. 

247. Why a Change of Climate May Be Beneficial. — The 
climate of the Southwest is chiefly beneficial during the win- 




Fig. 181. — Sleeping porch. 
(Courtesy of Dr. 8. A. Knopf.) 

ter months because one is most comfortable there when out of 
doors and, therefore, is inclined to remain out of doors. Even 
when indoors, one is most comfortable with the doors and win- 
dows wide open, therefore, the doors and windows are left 
open. In the severer climate of the North, during our waking 
hours and when engaged at ordinary occupations, we can not 
be comfortable with doors and windows open. We must, then,. 
condition the cuir to approximate the ideal climate. During 



232 THE SEASONS— CLIMATE AND HEALTH 

our sleeping hours, however, we. can be comfortable with open 
windows by using sufficient covers. We should, therefore, 
learn to sleep, summer and winter, with open windows and in 
the pure outside air. 

Living and Sleeping in the Open Air 

248. Open-air Rooms. — The open-air treatment has been 
found very beneficial in the treatment of both tuberculosis and 
pneumonia. In fact, the patient suffering from either of these 
diseases frequently lives and sleeps continually in the open air. 
There is every reason for believing that such open-air living is 
equally beneficial as a preventive measure. Well informed 
people have become convinced of this fact and many modern 
houses are being constructed with open-air living rooms, with 
sun rooms, and with open-air sleeping rooms. 

It is usually an inexpensive matter to construct a sleeping 
porch such as shown in Fig. 181. Many houses have porches 
which may be easily screened in for living purposes. 

Many devices have been perfected, especially for the accom- 
modation of tubercular patients who can not afford to build 
sleeping porches or who live in rented houses. Most of these 
devices are fitted to the open window in such a manner as to 
permit the patient to breath the cool, fresh, outside air while 
resting and sleeping. One such device is a window tent in 
which the patient can be kept in the open air, and which can 
be folded up out of the way when not in use. This window 
tent has a celluloid window which enables the patient to see 
all that takes place in the room. Such devices are very useful 
for several reasons: (1) They are easily attached to, and re- 
moved from any window; (2) they are economical because 
they prevent the loss of any considerable amount of heat from 
the room; (3) in case of severe sickness, the attending nurse 
and the members of the patient's family are able to use the 
room with comfort even in the severest weather ; at the same 
time the patient really lives -in outside air. 



CHAPTER V 
VENTILATION 

I. PRINCIPLES OF VENTILATION 

249. Need of Ventilation. — While the beneficial effects of 
outdoor life are being more and more recognized, still many 
people must necessarily spend much of their lives indoors. 
School children must spend many hours each day in the 
schoolroom. Factories, shops, stores, and offices are filled with 
working men and women who find it impossible to spend much 
time in the open air. Often their chief recreation is a visit to 
an overcrowded theater or moving-picture show where ade- 
quate ventilation is seldom provided. Even when at home few 
people enjoy fresh air. Relatively few houses have been con- 
structed with any recognition of the fact that fresh, pure air 
is of even greater importance than is warmth. For these rea- 
sons, what constitutes good ventilation and how it may be ob- 
tained should receive careful study. 

250. Composition of Pure Country Air. — Pure country air 
is composed chiefly of nitrogen, oxygen, carbon dioxid, and 
water vapor. The proportions of these constituents vary 
slightly from day to day and at different places, by far the 
greatest variation being in the amount of water vapor present. 
Pure country air consists of about the following proportions : 

Nitrogen about 77 per cent, by volume 

Oxygen about 21 per cent, by volume 

Carbon dioxid about 0.03 per cent by volume 

Water vapor — variable, from 0.3 per cent, to 3 per cent, by volume. 

In addition to these constituents of air there are usually 
present more or less dust, smoke, pollen from plants, and mi- 
croorganisms of different kinds. 

233 



834 VENTILATION 

251. Effect of Breathing upon the Composition of Air. — 

When man, or any animal, breathes this air, oxygen is con- 
sumed and carbon dioxid and water vapor are given off. 
When many people are gathered together in a closed, nearly 
air-tight room for some time, the air becomes much changed. 
We say that the air becomes vitiated. If some of those pres- 
ent are suffering from colds, pneumonia, tuberculosis, or other 
communicable diseases, the disease-producing germs (see 
Chap. VI) are certain to be present in the air. 

252. Theories Regarding Vitiated Air. — For many years 
the most objectionable factor in vitiated air was supposed to be 
small amounts of poisonous volatile matter, organic com- 
pounds, expelled from the lungs with the breath. This sup- 
position gave rise to the term crowd poisoning. Some years 
ago doubt arose as to the correctness of this supposition. Very 
careful experiments by skillful investigators employed by the 
government, failed to show the presence of this supposed ob- 
jectionable matter. Few scientists now believe in the crowd 
poison theory of vitiated air. It is now generally believed 
and taught by teachers of hygiene and sanitary science, that, 
as far as there is any offensive odor in the breath, it is prob- 
ably due to decayed teeth, effects of catarrh, decomposition of 
food in the mouth, or disordered stomach. 

Moreover, it is now believed that most of the unpleasant 
odors noticeable when any crowd gathers indoors come from 
the unclean bodies and clothing of those present. The skin 
of even the cleanliest person is constantly giving off waste 
material. A considerable portion of the waste materials of the 
body is given off through the pores of the skin. The offensive 
odors so characteristic of theaters, moving-picture shows, 
schoolrooms, auditoriums, and churches are now generally be- 
lieved to be caused chiefly by excretions from the skin, not 
from the lungs. In general, the theory of crowd poison has 
been abandoned. 

253. Theories Regarding Ventilation. — As already stated, 
pure country air usually contains about 0.03 per cent., or 3 



PRINCIPLES OF VENTILATION 235 

parts in 10,000, of carbon dioxid. It was assumed many years 
ago that air had become too vitiated for use when the propor- 
tion of carbon dioxid had been increased more than about 0.03 
per cent., or 3 parts in 10,000, due to breathing, i.e., when the 
proportion of carbon dioxid had been increased from 0.03 per 
cent, to more than 0.06 per cent. While it has been conclu- 
sively proved that the breathing of air containing as much as 
5 per cent., or 500 parts in 10,000, of carbon dioxid, has not 
the slightest depressing effect, still the old rule laid down years 
ago is the rule which controls in nearly all ventilating systems 
today. Even those who admit that a large amount of carbon 
dioxid in the air is harmless and that the theory of crowd 
poison can not be proved, still maintain that the percentage 
of carbon dioxid in the air is a good indication of the whole- 
someness or degree of vitiation of the air. 

254. Calculation of the Amount of Fresh Air Needed per 
Minute by Each Person. — If we admit that the amount of 
carbon dioxid in the air produced by breathing must not be 
permitted to rise above 0.03 per cent., or 3 parts in 10,000, we 
need only to know how much carbon dioxid is exhaled per hour 
by each person in order to determine the amount of fresh air 
which must be supplied him. This is easily calculated as fol- 
lows: Physiologists tell us that the average amount of the 
tidal air, i. e., of the air inhaled and exhaled at each breath, 
is from 20 to 30 cu. in. and that a person ordinarily breathes 
about 17 times per minute. Now if a person does breath 17 
times per minute and exhales 25 cu. in. at each breath, he ex- 
hales 17 times 25 cu. in. or 425 cu. in. of air each minute, or 
25,500 cu. in. per hour. 

Many analyses of exhaled breath show that it usually con- 
tains about 4 per cent., by volume, of carbon dioxid. Now 4 
per cent, of 25,500 cu. in. is 1,020 cu. in. Since there are 1728 
cu. in. in a cu. ft., it is evident that a person ordinarily ex- 
hales about 6/10 of a cu. ft. of carbon dioxid each hour. 

Now, if people are right in assuming that the air in the room 
must be so diluted by the admission of fresh air that the pro- 



236 VENTILATION 

portion of carbon dioxid derived from the breath shall not be 
greater than .03 per cent, or .0003 of the whole, we see that 
the .6 of a cu. ft. of carbon dioxid must not be more than .0003 
of all of the air admitted to the room for each person during 
the hour. If, then, .6 of a cu. ft. is 3/10,000 of the whole, 
1/10,000 is 1/3 of .6 or .2 cu. ft. and 10,000/10,000, or all of 
the air admitted, must be 10,000 times .2 cu. ft. which is 2,000 
cu. ft. per person each hour. 

Several years' ago, Massachusetts enacted a law requiring 
that all schoolrooms should be ventilated on practically this 
basis. It was soon discovered, however, that such a require- 
ment meant that practically every schoolhouse in the state 
would have to be rebuilt or remodeled. A compromise was 
therefore effected by which all schoolrooms were to be supplied 
with 1800 cu. ft. of fresh air per person each hour. Several 
©ther states have followed the example of Massachusetts. It is 
now common practice to provide 1800 cu. ft. of fresh air per 
person each hour in modern buildings. This means that, if a 
schoolroom contains 30 pupils and has a fresh air inlet of 
4 square feet that the air must enter at the rate of 3.75 ft. 
per second. This is about the same rate of motion as that of 
wind blowing 2% miles per hour, a very light breeze. (Prove 
the correctness of this calculation.) 

255. Error of This Theory of Ventilation. — Students of 
sanitation are now generally agreed that this theory of ven- 
tilation, namely, that air is necessarily so vitiated as to be un- 
wholesome if it contains more than 0.06 per cent, of carbon di- 
oxid, i. e., 0.03 per cent, as in pure country air plus 0.03 per 
cent, from breathing, is not scientifically well founded. They 
are raising the question whether the system of ventilation in 
common use is, after all, the best. Some are inclined to ques- 
tion the necessity of providing so much fresh air as 1800 cu. ft. 
per person each hour. Nearly all are convinced that we should 
give much more attention to temperature, to keeping the air in 
the room in motion, and to the proportion of water vapor in 



PRINCIPLES OF VENTILATION 



237 



the air than we are now giving, and that possibly these condi- 
tions are of even greater importance than the proportion of 
carbon dioxid. 

In order to understand the reason for this growing belief 
we must consider the total lung capacity of a person and the 
volume of air he ordinarily inhales and exhales at a breath. 
The following diagram adapted from Colton's Physiology will 
aid us in our study. 



i 




















COMPLEMENTAL AIR. 




a '& 












120 cu. in. 




3 'H 




Air that can be, but seldom is, 








taken in. 




o £ 








o '+, 








T* 3 








<M o ^ 








1-* 




TIDAL AIR. 20 to 30 cu. in. 




t— i -m 




Taken in and sent out at each 




O a3 




breath 4% carbon dioxid, 16% 








oxygen 


t>0 


O a) 




fl. 


rQ 






3 






RESERVE AIR. 




H * 






a> 


M « 






£ 


>t5 




100 cu. in. 




*-( 




Air that can be, but seldom is, 


v. 2 
•2 o 


^ 




driven out, 








about 5% carbon dioxid and 15% 






oxygen. 


1* 




RESIDUAL AIR. 


C3<N 




100 cu. in. 


a> 
fee 
c3 




Air that can not be driven 






out, 


<3 




at least, 5% carbon dioxid and 








not more than 15% oxygen. 





Diagram Illustrating Lung Capacity 



238 VENTILATION 

From this diagram, we see that the average amount of air 
in the lungs is 210 to 215 cu. in., while the tidal air is only 20 
to 30 cu. in. Now, as already stated, it is known that exhaled 
tidal air contains about 4 per cent, carbon dioxid. It must be 
remembered that the exhaled tidal air is the very purest air in 
the lungs. The 100 cu. in. of reserve air is somewhat mixed 
with the 30 cu. in. of tidal air and therefore diluted by it. 
But the 100 cu. in. of residual air, being the air in the ves- 
icles, or air cells, of the lungs, is but slightly altered in compo- 
sition by each inflow of tidal air. Considering these facts, 
authorities agree that the amount of carbon dioxid in the resid- 
ual air can not be less than 5 per cent. Now this residual air 
in the lung cells, or vesicles, is the air which receives the carbon 
dioxid from the blood and gives up oxygen to the blood. In a 
very true sense, it is almost wholly this residual air upon which 
the efficiency of our respiration depends. 

From the preceding facts we see that the lungs contain con- 
stantly over 200 cu. in. of air (100 cu, in. being reserve air and 
100 cu. in. being residual air) containing, at least, some 5 per 
cent, of carbon dioxid. It is evident, therefore, that it matters 
little whether the 20 to 30 cu, in. of tidal air contains 0.04 per 
cent, or 0.06 per cent, or even 4 per cent, of carbon dioxid. 

256. Same Reasoning Applied to the Other Constituents 
of the Air. — Fresh air is about 21 per cent, oxygen. Exhaled 
air is known to be about 16 per cent, oxygen. Evidently the 
oxygen in the residual air in the lungs can not be more than 
about 15 per cent, oxygen. Now, experimenters have shown 
that a person feels no discomfort when breathing air contain- 
ing no more than 15 per cent, oxygen. We are, therefore, 
forced to the conclusion that it is not the effect of breathing 1 
air with an increased percentage of carbon dioxid, nor with a 
decreased percentage of oxygen, nor of breathing air contain- 
ing " crowd poison" which constitutes the chief cause of the 
evil effects of living in an atmosphere of vitiated air. Inves- 
tigators have come to believe that other factors have quite as 
much bearing upon the problems of ventilation. 



PEINCIPLES OF VENTILATION 239 

257. Relation of Humidity of Ventilation. — Exhaled air 
contains much moisture — it is nearly saturated at blood tem- 
perature, or 98° F. Our bodies also give off considerable 
quantities of moisture in the form of perspiration through the 
skin. Tn poorly ventilated rooms where crowds gather, the hu- 
midity of the air rises rapidly. The result is that the evap- 
oration from the skin is checked and we soon become uncom- 
fortable. This effect of increased humidity is often greatly 
aggravated by increase in temperature due to the heat given 
off from our bodies. Taken together, the three conditions: 
(1) high humidity, (2) high temperature, and (3) foul odors 
soon produce headache and a feeling of weariness and exhaus- 
tion. Many recent experiments indicate that these three con- 
ditions of the air, high temperature and high humidity, and 
disagreeable odors in crowded, ill-ventilated rooms are large 
factors in producing what we know as vitiated air. 

258. Control of the Temperature of the Body. — The tem- 
perature of the human body in health is maintained with great 
constancy at 98%° F. No matter what the fluctuations of ex- 
ternal temperature, the mechanism of the human body is so 
delicately adjusted that, in health, it perfectly corrects the 
effects of all temperature changes. If the external tempera- 
ture is low, the temperature of the body is kept up by an in- 
crease of heat production within the body. If the external 
temperature is high, the temperature of the body is kept down 
by the cooling device of increased perspiration, and the conse- 
quent increased surface evaporation and cooling. (Art. 12, 
Ex. 10 ; Art. 13, Law V and Art. 179.) But any effort which 
the body must thus put forth to counteract external tempera- 
ture is necessarily a drain upon the vital forces of the body. 

259. Metabolism. — By metabolism we mean a sort of 
double process: On the one hand, the living cells of the body 
are built up and nourished by the food materials assimilated. 
On the other hand, it includes the breakdown of some of the 
living material of the cells into waste products. This latter 
phase of the process is always accompanied by the liberation 



240 VENTILATION 

of energy. It is a term by which we express the entire pro- 
cess of nutrition, both the building up and the nourishment of 
the living cells and the production of energy. This whole 
process of metabolism, however, is closely connected with the 
control of bodily temperature. 

260. Effect of External Temperature upon Metabolism. — 
In studying the effect of external temperature upon metabol- 
ism, experimenters have found that there is a certain tempera- 
ture best suited to stimulate metabolism, and therefore best 
suited to keep the person healthy and comfortable. That best 
external temperature varies with the age, health, and occupa- 
tion of the person. It is for this reason that we take so much 
pains to keep our houses and our schoolrooms^ ©ur churches 
and our stores comfortably heated. 

The experience of stockmen shows that stock exercising but 
little, as is usually the case with dairy cows and with beeves 
and hogs being fattened for the market, thrive best when the 
temperature is moderate. Extremes of temperature^ either 
high or low, reduce the flow of milk in the dairy cow and tend 
to prevent the fattening of the beef -cattle and hogs. In each 
case, nourishment taken by the animal is expended in effect- 
ing the control of bodily temperature. "We also know that 
work horses are not able to do so much work in extreme tem- 
peratures as in moderate temperatures, although the best tem- 
perature for the horse at hard work is much lower than when 
at rest. 

261. The Ideal Temperature of Indoor Air. — The best tem- 
perature for indoor air depends largely upon the occupation 
and dress of the occupants. The proper temperature for a 
gymnasium or a factory would certainly not be the proper tem- 
perature for a schoolroom or a church. Even the best temper- 
ature for a schoolroom or a church might prove to be too low 
a temperature for the home, owing to the fact that most people 
are likely to be more warmly clad when at school or church 
than when at home. 

As will later be shown, the relative humidity of the air in the 



PRINCIPLES OF VENTILATION 241 

room also largely determines the proper temperature. Rea- 
sonably moist air at 65° F. is as comfortable as very dry air 
at 70°. The temperature usualy demanded by Americans is 
several degrees higher than that preferred by the English and 
Germans. Our o^vvn plrysical condition also largely determines 
the most agreeable temperature. In the morning when our 
vitality is highest, we are comfortably warm at a temperature 
which is uncomfortably low in the evening when our vitality 
is lowest. Still another factor affecting the most agreeable 
temperature of air is that of air movements. Air in rapid 
motion must be a few degrees warmer than quiet air in order 
that we may be comfortable. Why? (See Art. 167.) 

The best temperature, then, depends upon many factors 
such as the occupation, dress, physical condition, and tempera- 
ment of the occupants of the room, on the one hand, and the 
humidity and movements of the air, on the other hand. The 
effect of air motion and of high or low humidity should be 
further studied. 

262. Some Changes in Temperature are Desirable. — A 
German, Fliigge, seems to have proved that a perfectly uni- 
form temperature is not desirable. Many students of ventila- 
tion now maintain that reasonable changes in temperature are 
necessary to stimulate us and to keep our physical and mental 
powers alert, awake, and active. A perfectly uniform temper- 
ature, even though it be the most agreeable, lacks the stimulat- 
ing effect of a reasonably fluctuating temperature (see Arts. 
159, 245 and 260). 

263. Effect of Air Movement. — Dr. Leonard Hill of Lon- 
don and others, have shown that proper air movement is a 
large factor in ventilation. Dr. Hill placed eight healthy 
medical students in a small, air-tight, glass-sided box, or cage, 
4% ft. square and 8 ft. high. In a few minutes they became 
very uncomfortable. The temperature of the air in the cage 
had risen to 85° F. and had become nearly saturated with 
moisture. The air then contained about 4 per cent, of carbon 
dioxid and only about 15 per cent, of oxygen. Three electric 



242 VENTILATION 

fans in the top of the cage were then set in motion, causing 
the air to move rapidly. The students were soon greatly re- 
lieved and became again fairly comfortable, although the com- 
position and the temperature of the air remained unchanged. 

Students of ventilation generally agree that quiet air, no 
matter how pure it may be or what its temperature and rela- 
tive humidity may be, does not furnish adequate ventilation 
for the body. In such cases, an envelope of highly heated, 
highly humidified air accumulates within one's clothing. 
Moreover, when many people are quietly seated in a room 
containing quiet air, as in the case of a schoolroom or a church, 
there is a strong tendency toward the forming of a layer of 
impure exhaled air at the height of the "breathing zone," i.e., 
at the- height of their faces. Authorities now agree that the 
air in any room should be kept moving with such rapidity that 
the air motion is perceptible to all. 

A careful study of the relation of air motion to ventilation 
has led Dr. W. A. Evans of Chicago to declare that, "A drafty 
room is a healthy room — a windy city is a healthy city. ' ' 

264. Importance of Proper Humidity. — It is now a gener- 
ally accepted theory that just as there is a best average tem- 
perature from which there should be no great variation for any 
long period of time, so there is a best humidity from which 
there should be no great or sudden variation. Dr. Hill's stu- 
dents, enclosed in their cage, soon raised both the temperature 
and the humidity to such a point as to cause great discomfort. 
The heat from their bodies caused a rapid rise in the tempera- 
ture of the confined air, while the moisture from their breath 
and from perspiration from their bodies soon raised the hu- 
midity nearly to the point of saturation. High temperature, 
too great humidity, still air, and offensive odors were prob- 
ably the chief causes of their discomfort. Exactly in the same 
manner, the air in a crowded, ill-ventilated room is likely to be 
at too high a temperature, the humidity is likely to be too high, 
the air is almost certain to have but little motion, and soon 
offensive odors become noticeable. 



PRINCIPLES OF VENTILATION 243 

Dr. Hill has stated the principle of good ventilation in a 
single sentence, thus: "The question of ventilation is pri- 
marily one of keeping the temperature, relative moisture, and 
movement of the air in proper state, so that the heat-regulat- 
ing mechanism of the body works without strain, and the 
nervous system is stimulated by pleasant cutaneous [skin] con- 
ditions and the circulation, respiration and metabolism of the 
body is invigorated." 

265. Humidity Sometimes too Low. — While in an ill-ven- 
tilated, crowded room the humidity is likely to be too high for 
the comfort and well-being of the occupants, in the best ven- 
tilated room or house, where artificial heating is required, the 
humidity is nearly certain to be too low, in cold weather, unless 
special effort is made to correct this tendency. It is generally 
accepted that the best indoor humidity is from 50 to 70 per 
cent. 

When air is cold, it takes but a small amount of water vapor 
to cause complete saturation; when air is heated to the tem- 
perature that is comfortable indoors, it takes many times as 
much water vapor to saturate it. Now, the average outdoor 
temperature for December, January and February for that 
portion of the United States lying north of the latitude of 40° 
is 25° or lower. But we usually heat our houses to nearly 
70°. It requires but 1.5 grains of moisture to saturate a cu. 
ft. of air at 25° while it requires about 8 grains to saturate a 
cu. ft. of air at 70°. If the outdoor air were fully saturated 
(which is seldom the case when the temperature is 25° ) and we 
admit that air into our houses or schoolrooms without adding 
more moisture, we shall then have but 1.5 grains of moisture 
to each cu. ft. Since the air at 70° must have about 8 grains 
of moisture to the cu. ft. to be saturated, we see that the air is 
but !•%, or less than % or 20 per cent., saturated. We speak 
of the air when in this condition as having 20 per cent, rela- 
tive humidity. 

During these three winter months the outside air in the 
northern portion of the United States has a relative humidity 



244 VENTILATION 

of about 80 per cent. If we add no water vapor to the air of 
our houses and schoolrooms, then, while we heat the air to 
70°, we are almost certain to find that while indoors we are 
living in an atmosphere heated to 70° but with a relative hu- 
midity of but 20 per cent, or possibly 25 per cent. When we 
step out of doors we are living in air at 25° but with a relative 
humidity of about 80 per cent. This means simply that when 
within doors we are living in very warm air that is exceedingly 
dry but when we step out of doors we are in air which is cold 
but usually very moist. 

We ought never to forget that if we do not provide for the 
addition of much water vapor to the air of a well-ventilated 
house anywhere north of the 40th parallel of latitude, that we 
are almost certain to be living in an atmosphere which contains 
but about Ys as much moisture as does the outside air in the 
very dryest climates of the inhabitable portions of the world. 

Such dry air is greedy for water vapor and robs every ob- 
ject in the room of all available moisture. As a consequence, 
the floor-cracks open, the furniture begins to creak, every 
joint in woodwork and furniture opens, even pianos made of 
the best kiln-dried wood show the effects of the* drought, 
leather backs of books become dry and sometimes crack, and 
house plants begin a struggle for life itself. 

266. Some Evil Effects of Such Dry Air. — Is such dry air 
beneficial to the human system? Physicians say it is not. 
They tell us that such excessively dry air causes rapid evap- 
oration from the nasal passages, and from the throat and bron- 
chial tubes, and thus keeps the mucous membrane in a con- 
stant state of irritation ; the mucous membrane thus irritated 
becomes swollen and spongy and affords an easy lodging place 
for disease germs. 

Even physicians who do not object to very dry air, or even 
see benefits to be derived from living in a dry climate con- 
stantly, are among those who object most seriously to this des- 
ert-like air in our homes and schoolrooms in northern latitudes. 
They object most seriously to the change we necessarily en- 



PRINCIPLES OF VENTILATION 



245 



counter when we are obliged to step from an indoor atmos- 
phere heated to 70° with a humidity of 20 per cent, into an 
outdoor atmosphere at 20° with a humidity of 80 per cent. 

267. Dry Air Requires High Temperature. — One has but to 
consider the effect of dry air upon the wet- and 
the dry-bulb thermometers to realize that a high 
temperature is necessary in order that we may 
be comfortable in a room having such low humid- 
ity. When the dry-bulb thermometer reads 70° 
and the relative humidity is 20 per cent., the 
wet-bulb thermometer reads 20° lower, i.e., the 
wet bulb then reads 50°. Now, the human body 
is constantly moist; more or less evaporation is 
constantly taking place from the skin. "While 
the clothing, by enclosing an envelope of air 
about the body, checks this evaporation somewhat, 
still, if the air in the room is in as rapid motion 
as it should be, we feel decidedly the chilling effect 
of evaporation. One is more comfortable in a 
room heated to 65°, or even 62°, with the humid- 
ity 50 per cent, than in a room heated to 70° with 
the humidity 20 per cent. This is especially true 
if the air be in motion. For this reason many 
physicians now advocate the use of the wet-bulb thermometer 
only, to determine room temperatures. 



Fig. 182. 
— A home- 
made wet- 
bulb ther- 
mometer. . 



Any common house thermometer can be converted into a wet- 
bulb thermometer by suspending a 3- or 4-oz. bottle of water from 
the frame and wrapping the thermometer bulb with a wick of soft 
muslin (Fig. 182). Such a thermometer will closely indicate the 
actual temperature in which we are living. 



268. Large Amounts of Water Must Be Evaporated. — 
Many people, who have become convinced that higher indoor 
humidity is desirable than is usually obtained during the win- 
ter months in the northern states, find difficulty in evaporating 
the necessary amount of water. In fact, much larger quanti- 



246 VENTILATION 

ties must be evaporated than most people realize. By know- 
ing the temperature and relative humidity of outdoor air and 
the temperature of the indoor air of a well ventilated room 
one can easily calculate the amount of water which should be 
evaporated. Experience proves the correctness of such cal- 
culations. 

The air in the ordinary dwelling having 7 or 8 rooms can 
be kept reasonably moist, usually, by evaporating from 3 to 
6 gallons of water daily. There are usually but few people 
living constantly in such a dwelling; moreover, there is usu- 
ally more or less water evaporated in cooking and otherwise. 

Schoolrooms are often better ventilated than are dwellings. 
To humidify a schoolroom properly, north of the 40° latitude 
in the United States, and well ventilated, requires the evapora- 
tion of much more water. It is safe to say that such a school- 
room containing 30 pupils and well ventilated, can be equally 
well humidified only by evaporating from 10 to 30 gallons of 
water during the school day of 8 hours during the 3 winter 
months. 

Exercise 54. — Testing the Relative Humidity of the Schoolroom 

During the months when artificial heat is being used, the relative 
humidity of schoolroom air should be determined frequently. If a 
hair hj^grometer is used, it should occasionally be checked by using 
a wet- and dry-bulb hygrometer and be properly adjusted when 
found to be inaccurate (see Art. 181). 

269. How the Necessary Amount of Water May Be 
Evaporated. — Where stoves are used to heat the room, it is 
usually possible to place a pan of water having a large sur- 
face on the stove and thus secure sufficient evaporation. In 
such cases, however, the percentage of humidity in the room is 
likely to vary much. 

In buildings heated by steam it is generally possible to 
permit the live steam to escape from the system, thus furnish- 
ing the required water vapor. 

Where hot-water heating is used, small stoves to evaporate 



PRINCIPLES OF VENTILATION 



247 



the water appear to be the only adequate means of humidify- 
ing the air. 

Furnaces are generally provided with water pans set in the 
casings, but they usually have little value as humidifiers. 
Any device used as a humidifier which will not readily evapo- 
rate 1 or 2 qts. of water per hour, in a well- ventilated residence 
having 6 or 8 rooms, is inadequate when used anywhere in the 
United States north of the 40th parallel of latitude. Most 
furnaces are so constructed that it is possible to equip them 




Fig. 183.— Humidifier. 

with a more nearly adequate humidifier easily and at slight 
expense. Fig. 183 shows how such a humidifier may be in- 
stalled in a furnace by any furnace setter. A large, seamless 
galvanized iron or copper pan filled with clean sand is set 
on the top of the radiator of the furnace inside the casing. 
A galvanized iron pipe is passed through the casing. The 
inner end of this pipe is directly over the center of the pile 
of sand. The outer end of the pipe carries an "elbow," 
turned so as to open upward. A supply pipe (leading from 



248 VENTILATION 

the water system or from a supply tank) equipped with a 
valve for regulating the flow, is so adjusted that water drips 
into the upturned elbow. The operator can see exactly how 
fast the water is being supplied, and the amount delivered by 
the supply pipe per hour can be determined at any time. 

Such a humidifier is nearly automatic in its operation. 
The sand forms a reservoir which is capable of holding a large 
amount of water. But it is evident that the sand becomes 
heated when the fire is burning up freshly. This heated sand 
then continues to evaporate water even when the fire has died 
down. In practice it is found that the humidity of the air 
delivered to the room above a furnace equipped with such a 
humidifier is fairly constant. 

270. Humidifying the Air of Schoolrooms. — The humidify- 
ing device which is adequate for ordinary schoolroom use 
north of the 40th parallel of latitude must be capable of evapo- 
rating about 2 gal. of water per hour for each room. To 
evaporate this amount of water is difficult. Nevertheless, 
many schoolroom heaters are so constructed that a humidifier 
similar to that shown in the last article may be installed 
with good results. 

271. Summary. — 1. "When is Air Vitiated? 

When its temperature is too high, when its humidity is too 
great, when foul odors are noticeable, or when it lacks motion 
so that one's body is continually wrapped in an envelope of 
unchanged air. The air may also be too low in temperature, 
or have too low humidity for good health and comfort. Any 
ordinary increase in percentage of carbon dioxid, or any 
ordinary decrease in percentage in oxygen is now considered 
relatively unimportant. 

2. Why Does Vitiated Air Produce Immediate Dis- 
comfort ? 

Because too high or too low temperature, or too high or 
too low humidity, or the lack of movement of air cause a 
disturbance of, and overtax the heat-regulating mechanism of 
the body, and fail to stimulate properly the respiration, cir- 



PRINCIPLES OF VENTILATION 249 

dilation, and metabolism of the body. Vital energy is being 
consumed and when carried to extreme, great discomfort and 
physical exhaustion results. 

3. Why is Continuous Living in Vitiated Air to be 
Avoided? 

Because disturbance of metabolism means decreased vitality. 
Decreased vitality means decreased power of resistance to 
disease. Moreover, conditions which produce vitiated air are 
generally favorable for the spread of infectious diseases. 

4. How is Air to be Kept from Becoming Vitiated ? 

It is not enough that the carbon dioxid in the air be kept 
down to 0.06 or 0.07 per cent, and the oxygen be kept up to 
20.5 per cent. These conditions may be worth while, but in 
addition, the wet-bulb temperature should be kept near the 
point of greatest comfort, which will vary probably from 50° 
or 55°F. for the gymnasium, work shop and factory to 65° 
or 70°F. for the home library; the humidity should be main- 
tained at 50 to 55 per cent., if possible, and the air should 
be kept in constant motion, this motion being sufficient to 
produce a pleasant, stimulating sensation very much like that 
of the early summer breeze. 

Some authorities insist that moderate fluctuation in tem- 
perature is preferable to constant temperature. They prefer 
to have the room frequently "flushed out" to any system of 
ventilation based upon the constant dilution of the vitiated 
air (see the next section). Dr. W. A. Evans says, "A ven- 
tilating system based on the dilution of breathed air is in- 
efficient and, at the same time, expensive. It is wasteful 
because it requires 2000 cu. ft. of fresh air per person per 
hour, while, if the temperature is kept down, the humidity up 
and the room blown out from time to time, a much less 
quantity gives better results." 

5. What Then is the Real. Purpose of Ventilation? 
Adequate ventilation prevents the accumulation of vitiated 

air about the body, thereby securing those conditions which 
are favorable to normal metabolism and the highest possible 



250 VENTILATION 

vitality. Secondly, in crowded rooms it is highly desirable 
to change the air either rapidly (constant dilution system) or 
frequently (flushing out system) because it is likely to be more 
or less laden with unpleasant odors and disease germs. 
II. SYSTEMS OF VENTILATION 

272. How Ventilation Was Obtained in Colonial Days. — 
"With all its faults, the old fireplace of colonial days had its 
advantages. Even the one room in which the fireplace was 
located was rarely overheated. That room was certainly 
supplied with an abundance of fresh air. Great volumes of 
air swept up the wide, open-throated chimney, to be replaced 
by fresh air which crept in through the numerous cracks 
between the logs or around the loosely fitted windows and 
doors. This was all in marked contrast to our modern houses 
with their nearly air-tight walls, heated by means of stoves or 
radiators, often with no provision whatever for the entrance of 
fresh air or the exit of foul air. It is a fact worth noting that 
although the colonists did suffer greatly with the cold they did 
not suffer as we do today with Golds and pneumonia. 

273. Modern Systems of Ventilation. — Even the humblest 
dwelling, heated by means of stoves, may be fairly well ven- 
tilated by being flushed out at frequent intervals by throwing 
open doors or windows. Besides this flushing method, there 
are several systems of ventilation in more or less common use 
all of which are based upon the constant dilution of the 
vitiated air. They all fall into one or the other of two classes ; 
Natural, or Gravity System, and the Forced System. 

Systems of Ventilation 
1. Natural or Gravity System. 2. Forced Systems. 

(a) By means of doors and (a) Air forced in by fans, 
windows. "Plenum System." 

(b) By means of special air (b) Air moved by suction 
shafts. fans. 

(c) Combination of propul- 
Generally used in private resi- sion and suction. 

dences and small buildings. Generally used in large public 

buildings. 



SYSTEMS OF VENTILATION 



251 



274. Ventilation of Dwellings. — The system of ventilation 
employed in dwelling houses is largely determined by the 
method of heating employed. When heated by means of 
stoves the dwelling is usually ventilated either (1) by frequent 
flushings* or (2) by window ventilation. The latter is a form 
of the gravity system. The cooler, outside air is permitted to 
flow in at the bottom of the window and force the warmer, 
vitiated, inside air out at the top of the window. In this 
manner the vitiated air is being constantly diluted. 




Fig. 184. — Indirect radiation. 

When the dwelling is heated by means of a furnace, the 
fresh air is admitted by means of a fresh-air flue, or intake, 
entering the base of the furnace (Art. 119). The circulation 
is maintained by the convection currents (Chap. II, Sec. IX). 
It is evident that an outlet must be provided for the foul air. 
The most efficient outlet is provided by an open grate, or 
fireplace, especially if a fire is maintained in it. Explain 
why this is so. 

When a dwelling is heated by steam or hot water it may 
be ventilated at the same time if what is known as the 

INDIRECT RADIATION SYSTEM is USed. 



252 VENTILATION 

In the direct system of heating by steam or hot water, the 
radiator stands in the room to be heated, usually in the cold- 
est portion of the room, beneath or near a window. No pro- 
vision is made for taking in fresh air; the radiator merely 
heats the air in the room. 

In the indirect system, the radiator is suspended beneath 
the floor of the room to be heated. It is surrounded by a 
sheet iron casing. From an opening in the outside wall a 
sheet iron pipe leads the fresh air to the box surrounding the 
radiator. Another similar pipe leads from the radiator box 
to the register. When the air around the radiator is heated 
it becomes lighter and is forced up through the register by the 
colder, outdoor air or by the colder air of the room as shown 
in Fig. 184. 

275. Ventilation of School Buildings. — The problem of 
ventilating school buildings is also largely determined by the 
size of the building and the mode of heating. The usual mode 
of heating a one-room school is by means of a stove, occa- 
sionally by means of a furnace, and rarely by hot water or 
steam. The heating of large, many-roomed school buildings 
is usually by means of steam heat, sometimes by hot water, 
rarely by means of stoves or furnaces. 

Exercise 55. — A Study of the Ventilating System of the School 

Building 

The class should examine carefully the heating and ventilating 
system of the schoolroom or school building. Note where the fresh 
air is admitted, how it is heated. Can fresh air enter the room un- 
less provision is made for the impure air to escape? Find where 
and how the impure air is permitted to escape from your school- 
room. Write a short description of the way your schoolroom is 
heated and ventilated. 

276. Heating and Ventilating the Several-room School 
Building. — Forced systems of ventilation are generally used 
in modern school buildings containing several rooms. As was 
the case in the one-roomed school, so here we find that the 
heating and ventilating systems are usually combined. "When 



SYSTEMS OF VENTILATION 



253 



such large quantities of air must be moved the gravity system 
is not adequate, the forced system must be employed. More- 
over, school buildings containing several rooms are likely to 
be heated by steam and steam power is therefore available for 
driving the fan, or blower, if desired. 

Forced systems of heating and ventilation may be of the 
propulsion type, known as the plenum system, or it may be 
the suction system, or a combination of the two systems. 

277. The Plenum System. — In the plenum system the 




Fig. 185. — Showing the plenum system for warming and ventilating 
a school building. A tempering stack is shown at the right, next (to 
the left) is an air washer to insure pure and reasonably moist air, 
next is a fan or blower, and following that a re-heater, which warms 
the air to any desired temperature. 



blower or fan is usually placed in the basement and forces all 
the fresh, heated air needed for heating and ventilation 
through air ducts into the various rooms. The air in all the 
rooms is, therefore, somewhat compressed, that is, the air in 
all the rooms is under somewhat greater pressure than is the 
air outside the building. Hence the name plenum meaning 
full. 

Figure 185 shows the usual construction of the plenum type 
of heating and ventilating systems. The fresh air enters at 
the window A. It then passes through a bank of steam 



254 VENTILATION 

pipes called the tempering coils, or tempering stack, B. 
Here the temperature of the air is raised to about 65 °F. It 
then passes through a washer, a spray of water, C, which 
washes the air removing all dust particles and increasing the 
humidity. The air thus warmed to about 65°, washed and 
humidified, passes into the tempered air room, D. It then 
passes into the blower, E, which forces it, blows it, strongly 
to the left. The upper two-thirds of the exit from the blower 
contains another bank of steam pipes called the hot coils, or 
re-heater, F. Just beneath the hot coils is a horizontal par- 
tition, or false floor. The air from the blower may pass 
through the re-heater into the hot room, H, or it is equally 
possible for it to pass beneath the false floor directly into the 
second tempered air room, G. In both of these rooms, G 
and H, the air is under increased pressure due to the force 
with which the blower forces the air into them. The air in the 
hot room, H, however has been re-heated as it passed through 
the hot coils, F. The temperature of this heated air depends 
upon the outside temperature. It may be 80° or 85°F. on a 
mild day, or 110° to 120°F. on a cold day. The air in the 
tempered room, G, remains at about the same temperature 
as in the first tempered air room, D. Fro^m the rooms, G 
or H, or both, the air passes through the flue F, to the wall 
register, M, thence into the room to be heated. The foul air 
escapes from the room through the other wall register, N, into 
a flue which extends up through the roof. 

278. The Thermostat Control of Temperature. — The 
plenum system is operated on the principle of maintaining a 
constant temperature. It is necessary, therefore, to control 
the proportion of heated air from the hot room, H, and of 
tempered air from the tempered air room, G, which passes 
through the flue F, to any room. This control is accomplished 
automatically by a thermostat system. 

In the plenum system all of the air which enters the build- 
ing is fresh, outdoor air. The thermostat system is, therefore, 
merely an ingenious device by which the tempered air and the 



DUST AND ITS DANGERS 255 

hot air are mixed in the proper proportions so as to keep the 
air in the room at the desired temperature. 

279. The Suction System of Heating and Ventilating. — 
In the suction system the fan, or blower, is usually placed in 
the attic of the building. The purpose is to suck the air out 
of the building (see Art. 284). The air within the room is 
then under less than 1 atmosphere of pressure. The suction 
system is not often used alone ; it is often used in connection 
with the plenum system to secure more perfect ventilation of 
laboratories, toilet rooms, kitchens, or other rooms. 

III. DUST AND ITS DANGERS 

280. Live Dust and Dead Dust. — All dust may be classified 
as live dust or dead dust. "While all dust looks alike to the 
housekeeper and the janitor, it is now known that the chief 
danger to man lies in coming in contact with live dust. We 
shall see in Chap. VI that many communicable diseases such 
as tuberculosis, pneumonia, colds, grippe, diphtheria, and 
others are caused by living microorganisms. These and other 
similar organisms constitute live dust. Most, if not all, of 
these disease germs die quickly when exposed to direct sun- 
light or high temperature. Therefore, the dust blown in from 
the street, or the fine ashes coming from the stove or furnace, 
can not be looked upon as particularly dangerous, no matter 
how annoying such dust may be. 

281. House Dust. — House dust is almost certain to consist 
of both live dust, living organisms, and of dead dust. It is 
of great importance, therefore, that so far as possible all dust 
be removed from rooms where people live or congregate, not 
simply because it looks bad, but principally because it en- 
dangers the health of the occupants. Ordinary sweeping with 
a broom or carpet sweeper does not remove the most dangerous 
portions of the dust. Dusting the room with a dry dusting 
cloth does not remove much of the dust. Such methods 
remove only the large particles of dirt which are not particu- 



256 VENTILATION 

larly dangerous, merely unsightly, and remove the finer dust 
from the more exposed surfaces allowing it to settle again in 
the unobserved places. No system of house cleaning and dust- 
ing is effective or much worth while^ so far as health of the 
occupant is concerned, unless it really removes the dust from 
the house. 

Exercise 56. — Observing Dust in the Air of a Room 

Darken a room by drawing the window shades (either a living- 
room at home or the schoolroom will do) leaving a small crack at 
one window through which the direct sunlight may enter. Observe 
the dust particles floating in the air. Why is it that they now be- 
come visible? With a broom sweep the floor or carpet near the 
window. Does the amount of dust floating in the air increase? 
With a dry dusting cloth wipe the walls or furniture and shake the 
cloth in the ray of sunlight. Note the result. 

Remember that this is the air which we are constantly 
breathing and which is constantly coming into contact with 
our food as it is being prepared in the kitchen or served upon 
our dining table. 

282. Carpets, Drapery, and Bric-a-brac Dangerous. — Car- 
pets are exceedingly difficult to keep free from dust. Ordi- 
nary sweeping removes but little of the fine dust from the 
carpeted floor; much of the fine dust lodges in the carpet or 

passes through it. One has but to 
recall the condition of the floor as it 
appears after the carpet has been 
taken up for the annual or semi- 
annual cleaning, in a house where 
the floors have been cleaned by 
sweeping with a broom or carpet 
sweeper, to see that ordinary sweep- 
Fig. 186.— Carpet sweeper— ing is unsanitary. If the floors are 
type of vacuum cleaner. to \> e k ep t c l ea n by sweeping they 
should be oiled, painted or waxed and then covered with rugs 
which are easily removed and beaten. Such floors may be kept 
in a sanitary condition. Drapery and br' irac on the walls 




DUST AND ITS DANGERS 257 

are dust catchers and very difficult to clean. The more 
thoughtful people of today are using fewer bric-a-brac to 
decorate the walls and hang fewer draperies than people did 
a few years ago. The fewer dust catchers there are in any 
living room, or any sleeping room the easier it is to care for it 
and the more sanitary it may be kept. 

283. Vacuum Cleaning. — In recent years many devices for 
vacuum cleaning have been put upon the market. They 
range from simple, inexpensive devices, operated by hand, 




Fig. 187. — Hand Electric Vacuum Cleaner. 

or electricity, for use in private dwellings, to large, ex- 
pensive plants, operated by electric motors or steam engines 
for the cleaning of the largest hotels, railroad stations, office 
buildings, school buildings, and stores. They all operate by 
producing a partial vacuum. In most large types a tube or 
pipe leads from the machine to the cleaning tool. This 
cleaning tool fits closely to the carpet or other surface which is 
to be cleaned. Air pressure causes a strong current of air to 



258 VENTILATION 

rush into the vacuum carrying dirt and dust with it. On its 
way to the pump where the vacuum is produced, the dust- 
laden air passes through a thick, closely woven cloth, or is 
washed by a spray of water, thus removing all dirt and dust. 
The air which actually passes through the pump is, therefore, 
practically dust free. 

In the sweeper type (Fig. 186) the vacuum is produced by 
hellows, or movable diaphragms, operated by the friction of 
the wheels upon the floor or carpet. In this type of cleaner 
the cleaning tool is a part of the machine itself. 




Tig. 188. — A street vacuum cleaner. (By permission of the Municipal 

Journal. ) 

Many modern dwellings, churches, auditoriums, office 
buildings, stores and school buildings are equipped with 
•stationary vacuum cleaners. In such cases the machine is 
usually located in the basement and the suction pipes are run 
to the various rooms of the building. Rubber hose carrying 
the cleaning tool may be attached to the suction pipes at 
•convenient points throughout the building. In some cities 
vacuum cleaners have been successfully used in street clean- 
ing (Fig. 188). 

284. Meaning of Suction. — Many people use the word 



DUST AND ITS DANGEES 259 

suction without knowing its real meaning. The words 
suction and sucking are good, common English words, and 
express ideas not easily expressed in other words. When we 
use these words we ought, however, to know just what they 
mean. Suction does not mean drawing or pulling as many 
people believe. Sucking soda water up a straw does not mean 
drawing it up the straw. Liquids and gases can not be drawn 
or pulled ; they must be moved by being pushed. 

Definitions. — Suction is the process by y which a partial 
vacuum is produced into which a fluid, either a liquid or a 
gas, is forced by outside gaseous pressure, usually the pres- 
sure of the atmosphere. 

Sucking is the act of producing a partial vacuum into- 
which the surrounding atmospheric pressure tends to flow. 

When we suck soda water up a straw we merely enlarge the 
mouth cavity and thereby produce a partial vacuum into 
which the atmospheric pressure forces the soda water. When 
we clean a carpet by means of a vacuum cleaner, the tool fits 
tightly against the top surface of the carpet. In entering the 
tool the air must come up through the carpet; as it does so 
it carries all loose dust and dirt with it. 

Exercise 57. — A Study of Vacuum Cleaners 

Study several different types of home vacuum cleaners, determin- 
ing exactly how they work. Write a description of one or more of 
the cleaners studied. 



CHAPTER VI 

MICROORGANISMS— THEIR RELATION TO OUR 
FOOD SUPPLY, TO THE SOIL, AND TO OUR 
HEALTH 

285. The Energy of Living Beings. — Every living being, 
whether animal or plant, requires energy with which to carry 
on its life processes. All such living organisms get this nec- 
essary energy from foods. It is well known that the only 
living things which can manufacture food out of the simple 
materials found in air and in soil are the green plants (Art. 
373) . All foods and all food materials which can give energy 
to other forms of living things have first been in the form of 
green plants. The green plants are the food makers of the 
world. 

Since this is true, it follows that all animals and all non- 
green plants, such as molds, yeasts and bacteria, which we 
shall study in this chapter, must constantly be striving with 
each other for the food materials which have been produced by 
green plants. 

Most animals live upon about the same kind of food that 
man does. Many animals live upon corn, wheat, oats and 
other grains just as man does. Birds, mice and insects do not 
hesitate to help themselves to the food that man has collected 
for his own use and for the use of his domesticated animals. 

286. Plants That Attack Our Foods. — People do not gen- 
erally know, however, that the worst competitors man has for 
the food he wishes to keep in store are the non-green plants. 
We have all heard people complain that food, especially cooked 
food, spoils or decays. They speak in this way because they 
do not know that what really happens is that very small non- 
green plants are consuming our food as their food. These 
minute plants generally escape our notice because they are so 

260 



MICROORGANISMS 261 

small that they can be seen only by the use of the microscope. 
Because they are so small they are grouped together with a 
host of minute animals under the general name microorgan- 
isms — organisms that can be seen only with the help of the 
microscope. 

In Section I of this chapter we shall study some of these 
plant organisms and the conditions under which they grow 
most rapidly. "We shall also study the methods man has de- 
vised to ward off the attacks of the microorganisms upon our 
food supplies and upon other useful materials which we wish 
to preserve. We shall also learn that these little microor- 
ganisms are not altogether harmful to man. We shall find 
that they are often very valuable, for they consume materials 
which are worthless to man. They change all the organic 
waste materials which are produced where man and the higher 
forms of life exist back into the raw materials upon which 
green plants live. In this way they keep up the fertility of 
the soil. But for the work of these microorganisms in re- 
ducing the waste materials of man, of animal life and of _ the 
higher plant life back into raw or inorganic material — but for 
their work, all higher forms of life would soon perish from 
the earth. 

287. Saprophytes and Parasites. — The microorganisms of 
which we read in the last article live upon food supplies and 
the waste materials of man and the other higher forms of life. 
They do not live within the bodies of the higher forms of plant 
or animal life. They are called saprophytes {sapros, Greek 
meaning rotten and phyton, Gr. meaning plant). That is, 
saprophytes are plants which live upon dead or rotting 
materials. 

We shall see, however, that there are other microorganisms 
which live only within the bodies of man and the higher forms 
of animal and plant life. Such organisms are called para- 
sites. Modern medicine teaches that it is on account of the 
presence and activities of these parasites within the bodies of 
the higher animal and plant life that they suffer and often die 



•262 



MICROORGANISMS 



of bacterial diseases. This story will be told in Sec. II of 
this chapter. 

I. SAPROPHYTES— PLANTS WHICH LIVE UPON DEAD 
ORGANIC MATTER 

288. Plant Relationships. — It is a fact well known to bot- 
anists that the many different kinds of plants are really 
related to each other much as the different individuals of the 
human race are related. We group certain plants together 
because of their having strong likenesses and speak of all of 
the individual plants as belonging to a certain species. All 
of the plants belonging to a certain species have descended 
through long ages from a common ancestor. -We all know 








Fig. 189. — Bacteria. Ex- 
tremely small even when com- 
pared with yeast or mold. 



Fig. 190. — Yeast cells, show- 
ing the budding of the cells. 
Greatly enlarged. 



that the individual plants of a certain species are not exactly 
alike. As the ages go on, the plants of a certain species doubt- 
less will ever tend to vary in many ways. 

If we think back through the ages to the time when a cer- 
tain individual plant gave a start to a certain species, we shall 
easily imagine that there were other individual plants grow- 
ing near by. Each of them resembled, more or less, the ances- 
tor of the certain species just mentioned. A few of those in- 
dividuals resemble each other very closely. The descendant 
plants from two or more of these ancestral plants which 
closely resemble each other will have certain resemblances 
today. It is such plants which have " blood relationships" 
which we group together in what we call a genus of plants. 



SAPROPHYTES 



26£ 



To compare with relationships as we know them in the human, 
race, a species of plants includes the brothers and sisters o£ 
a family; a genus of plants includes all of the near cousins; 
a family of plants includes all the closely related genera. 
By species of plant life we mean an inner circle of very closely 
related plants; by genera a somewhat larger circle which 
includes several species all more or less related; and finally, 
by family, a still larger circle including all the related species, 
of several genera. 

289. Basis of Classification of Plants. — In classifying 
plants into these groups, botanists rely mainly upon simi- 




A B 

Fig. 191. — Mold — mucor. A, common mold, often growing on bread! 
and fruit. B shows a diagrammatic representation of mucor, showing 
the profusely branching mycelium, and three vertical hyphse (sporo- 
phores), sporangia forming on 6 and c. 

larities in the organs and processes of reproduction. It is fair 
to suppose that plants which reproduce by the same methods: 
today have descended from a common ancestor. In classi- 
fying some of these minute plants into three classes, molds, 
yeasts, and bacteria, botanists depend chiefly upon a study of 
their different modes of reproduction. 

The ordinary method of reproduction among molds is by 
means of spores. The ordinary method of reproduction 
among yeasts is by budding. The only method of reproduc- 
tion among bacteria is by cell division. 



264 MICROORGANISMS 

We shall want to study each of these classes of plant life 
somewhat in detail. As we study them, these different modes 
of reproduction as well as other important characteristics will 
become clear to us (Figs. 189, 190, and 191). 

MOLDS 

290. Molds Reproduce by Means of Spores. — As has been 
stated, the usual way molds reproduce is by spores. As is 
true of all higher forms of life, the plant body of molds con- 
sists of many cells, some of which differ from others. Certain 
portions of the plant body -produce great numbers of small, 
usually oval-shaped cells, which the wind easily blows off 
and scatters broadcast when they are matured. These cells 
are called spores, and it is from them that new mold plants 
grow when these spores light upon suitable soil, and suitable 
conditions of warmth and moisture exist. The new mold plant 
thus produced always closely resembles the mother plant. 

This method of reproduction reminds us of the usual method 
of reproduction in the higher forms of plant life, i.e., by seeds. 
The botanist, however, sees a great difference between spores 
and seeds which we need not discuss here. 

291. A Study of Molds. — 

Exercise 58. — Growing Molds 

Soak several pieces of bread in water until they become saturated, 
and then place them under glass vessels where they will remain 
moist. Set the vessels in a warm place and observe daily for the 
growth of mold on the bread. When the mold first begins to grow, 
it will appear as a soft, white, felty mass over the surface of the 
bread extending up from the surface resembling a piece of very 
light gray fur. After a day or two, the mold will begin to show 
some color. It may be pink, green, brown, black, blue, or almost 
any color, depending on the kind of mold that you chance to get. 
The plant body of the mold is always of the whitish-gray color that 
appears first. The color, which appears later and which helps us 
to distinguish the different kinds of mold, is in the spores. 



SAPROPHYTES 265 

Exercise 59. — Collecting Molds 

Search the garbage can at home, the fruit and vegetable cellar, 
and the back yards of grocery stores for molds growing on decaying 
fruits and vegetables. Almost any decaying material of this kind is 
likely to contain mold, whether the mold is apparent on the exterior 
or not. Place the material collected in this way in moist, enclosed 
vessels for further growth of the mold. Transfer some of the spores 
from the different kinds of mold that you collect to fresh pieces of 
soaked bread and thus raise as many kinds of mold as you can on 
the bread. Note how rapidly the mold grows and how soon a new 
growth produces spores. Can you suggest some reasons why molds 
are able to grow so rapidly? Considering the fact that molds can 
grow only when supplied with an abundance of moisture, do you 
see that it is essential to the success of molds that they be able to 
grow rapidly and come to fruit in a short time? 

Exercise 60. — Study of Molds under a Microscope 

When you have a good collection of different kinds of molds, make 
a comparative study of them under the microscope. You will ob- 
serve that the plant body consists of numerous, very small and, 
usually, very much branched threads. These threads are called 
hyph.e (singular, hyplia) and the whole network formed by the 
branching hyphae is called the mycelium (Fig. 191). In some molds, 
you will note that the hyphae are broken up into distinct cells by 
numerous cross walls. In others these cross walls are missing and 
the whole hypha is one continuous tube-like structure. If you 
study under the microscope a very small piece of the pulp of a 
badly decayed apple or banana which shows some signs of mold on 
the exterior, you will find that the mycelium of the mold has com- 
pletely permeated the pulp of the fruit. 

292. Digestion by Molds. — We know that food generally 
needs to be digested before it becomes available as nourish- 
ment for a living organism and we know something of the na- 
ture of digestion. Molds digest their food in essentially the 
same waj^ as animals do bnt they have no organ like a 
stomach, or alimentary tract in which this process is carried 
on. The molds secrete, produce and give out, certain fluids 
called digestive enzymes. These enzymes diffuse, or spread 
out, into the material in which the mold is growing. These 



266 



MICROORGANISMS 



enzymes prepare the food materials for absorption and assim- 
ilation by the molds much as the gastric juice of our stomachs 
prepares the food materials in our stomachs for absorption 
and assimilation by the walls of our stomachs. We, perhaps, 
might well say that the entire exterior, or outside, surface of 
the mold is its stomach. 

Thus, when we say that molds have caused an apple to 
decay, we might describe more fully what happens if we were 
to say that the molds have digested and absorbed and grown 
on the foods contained in the apple. We can not say that the 
mold eats the apple for, as we commonly use that term, it 
involves chewing and swallowing and this the mold does not 





Fig. 192. — Aspergillus. 



Fig. 193. — Penicillium. A 
common mold. The spores give 
it a greenish color. 



do. In the light of this discussion of the way in which a mold 
gets its food, can you suggest how it is that the delicate 
hyphae of the mold are able to make their way through the 
solid pulp of an apple? 
293. Methods of Spore Production. — 



Exercise 61. — Microscopic Study of Molds 

After you have studied the mycelium of a given mold under the 
microscope, mount a little of the portion of it which is just be- 
ginning to show spores and observe the character of the structure 
which bears the spores. The spores are generally borne on vertical 
branches of the mycelium which extend some distance above the sub- 
stratum, or mass of food, within which the main body of the myce- 



SAPROPHYTES 267 

lium is growing. At the top of this vertical branch which is called 
a sporOphore, the spores are borne in different ways in different 
kinds of molds. The accompanying figures illustrate the manner in 
which some common molds produce spores (Figs. 191, 192, 193 and 
194). 

Note the countless number of spores that you get on your micro- 
scope slide from a very small quantity of the material. Remember- 
ing that these spores are always borne up in the air above the sub- 
stratum, and that they are light and powdery, do you wonder that 
the spores of mold are abundant everywhere? Do you see that the 
molds are highly fitted to compete with us for possession of our 
food? 

In this way, study all the different kinds of molds that you 
have collected. Your instructor will be able to tell you the 
names of several of the different kinds of molds that you study 
and you will be able to identify some of them by comparing 
them, as you study them, with the different figures in the text. 

Exercise 62. — Identifying Molds on Different Materials 

After you have learned to identify several different kinds of molds, 
select one or two of them and see how many different kinds of ma- 
terial you can find them growing on. If you select the common 
green mold, Penicillium, for example, you should find it growing 
011 a great variety of different substances (Fig. 193). Cheese, cured 
meats, stale bread, old clothing, old shoes, indeed, almost any kind 
of plant or animal matter may afford food for this mold. Note 
that the general appearance of a given mold varies considerably 
as it grows in different situations. 

294. Conditions Which Favor Mold Growth. — If we are to 

be successful in warding off the attacks which molds make on 
the things which we wish to preserve, we must understand the 
conditions which are favorable for mold growth. Everyone 
is familiar with the fact that molds do not grow on materials 
which are quite dry. One of the earliest methods which man 
ever devised for the preservation of food is that of drying it. 
A certain amount of moisture must be present before molds 
can grow at all and a considerable amount is necessary for a 
luxuriant growth. When there is barely enough moisture 




268 MICROORGANISMS 

present in a given material to support a mold growth, the 
mycelium development is very slight and there is little visible 
evidence of the presence of the mold except the spores. The 
spores are borne on very short sporophores and present a 
powdery appearance over the surface of the substratum. It 
is common to speak of mold when it presents this appearance 

as mildew. Mildew is simply 
mold which has grown on a 
scant moisture supply. During 
most of the year, the out door air 
and the air in houses is relative- 
ly dry. Consequently, dry ob- 
jects in this air are too dry for 
the growth of molds. In the 
Fig. 194.— Antenaria. Note da gult wea ther of the 

how differently it bears its . _ n . 

spores when compared with summer time, however, the air 
mucor, aspergillus, or peni- sometimes becomes so damp as 

to give sufficient moisture to dry 
objects, such as clothing, carpets, and the like, to permit a 
growth of mold on these materials. 

Clothing hung in closed closets and the carpets of unused 
rooms which are closed up, are more likely to suffer from 
mold growth during damp, warm weather than if they were 
well aired, for it has been found that air movement is detri- 
mental to the growth of mold. 

Molds will grow to some extent at comparatively low tem- 
peratures, some even growing a little at only a few degrees 
above freezing. For any rapid growth, however, a rather 
high temperature is usually necessary. We take advantage 
of this fact in keeping our food from molding between meals 
and over night by putting it into a refrigerator. "We should 
remember, however, that the temperature of a refrigerator 
is sufficiently high to permit of some mold growth, and for this 
reason we should not attempt to keep food in a refrigerator 
very long. 

The four necessary conditions for rapid growth of molds, 



SAPROPHYTES 269 

then, are: Plenty of moisture, quiet air, a moderately high 
temperature, and food. 

295. Effect of Mold Growth on Food. — Food is not neces- 
sarily ruined by the growth of mold in it. In fact, every time 
we eat an apple that is partly decayed, we are likely to eat a 
considerable quantity of mold which has already penetrated 
the apparently sound parts of the apple. Similarly, when we 
eat apple sauce, or other similar food, which has stood in a 
refrigerator for a day or more, we are likely to eat some mold 
even though we are unable to detect it. An abundant growth 
of mold in food will give it a changed flavor which we may 
not like, but we are not likely to be harmed in any way by 
eating food even when mold can be tasted in it. When mold 
grows in food, the food loses some of its value, for the mold 
consumes some of the food which we might otherwise have 
had, and our consumption of the mold does not wholly make 
up for this. Ultimately, the molds, and the bacteria which 
are likely to accompany them, will completely consume the 
food and render it worthless. On the other hand, the growth 
of some molds in certain foods greatly enhances their value 
by giving them a delicate flavor which we very much desire. 
If you have ever eaten Roquefort cheese, you have had expe- 
rience with one of these useful molds. 

YEASTS 

296. The Prevalence of Yeasts. — Yeasts have been used 
by man for raising bread and for making fermented liquors 
since before the time of historical records. Yet, notwith- 
standing this, the actual relation which yeasts bear to these 
processes was never clearly demonstrated until after the mid- 
dle of the nineteenth century. We do not even need to put 
yeast into fresh fruit juice in order to make a fermented 
liquor out of it, for yeasts, like mold spores, are widely dis- 
tributed and are always sure to be present wherever there is 
suitable material for them to feed on. Similarly, it is possi- 
ble to make raised, or leavened, bread without putting pre- 



270 MICROORGANISMS 

pared yeast into the mixture. Probably you have eaten what 
is called "salt rising" bread. This bread is made by putting 
a little salt into some milk and allowing it to stand in a warm 
place for a time, and then using this milk for mixing the bread. 
The salt keeps other organisms from growing in the milk, 
and wild yeasts fall into it and multiply until they are 
numerous enough to cause the bread to rise. 

In essentially these ways, yeasts have been used for many 
centuries, but it was not until after the perfection of the micro- 
scope that men were able to find out much about them. In 
recent years we have learned many interesting things about 
yeasts, but there are still many things that we do not under- 
stand about them. You will doubtless be interested in learn- 
ing some of the things that are known about these little plants 
that play so large a part in our lives. 

297. Study of Yeasts. — ■ 

Exercise 63. — Growing Yeast 

Mix about 2 tablespoonfuls of molasses with a quart of warm 
water in a glass vessel. Stir the mixture thoroughly and then add 
about one-half of a cake of compressed yeast, breaking the yeast 
cake into small particles. (If compressed yeast is not available, 
dried yeast cake will answer, but it will be very much slower in 
action.) If possible, keep the mixture at a temperature of from 
70° to 90° F. Note the bubbles of gas that soon begin to rise in 
the mixture. Mount a small drop of the mixture on a microscope 
slide and study under the high power of the microscope. Note the 
size, shape, abundance, and general character of the yeast plants. 
In this fresh mixture, you will probably not find any budding 
cells for, in the yeast cake, the plants are more or less dormant, or 
inactive. If you study in the same way an older mixture of the 
same kind which your instructor may have prepared a couple of 
hours or more before class, you will find many budding plants. 

Exercise 64. — Growing Yeast Produces Carbon Dioxid 

Fill a small bottle about two-thirds full with the yeast mixture. 
Fill another small bottle up to the neck with clear lime water. Put 
a one-hole rubber stopper into the bottle containing the yeast mix- 
ture and connect the two bottles by a U-shaped glass tube as shown 



SAPEOPHYTES 



271 



in Fig. 195. As the gas which you have observed rising from the 

yeast mixture accumulates above the liquid, it 

will be forced through the glass tube over into 

the limewater. Observe the white, milky cloud 

that forms in the limewater near the open end 

of the tube. The white substance which forms 

as the gas from the yeast mixture is forced into 

the limewater is essentially the same as common 

chalk. It is formed by the chemical action of 

carbon dioxid on limewater, and, therefore, its 

appearance here indicates that the gas which the 

yeast mixture is giving off is carbon dioxid. 

You are familiar with the fact that your own 

breath contains carbon dioxid. Take some fresh 

clear limewater in a small bottle or test tube and by means of a small 

glass tube, force your breath through the limewater. (Review Arts. 

75 and 76, especially Ex. 26,) 




Fig. 195.— Car- 
bon dioxid pro- 
duced by growing 
yeast. 



Exercise 65. — Growing Yeast also Produces Alcohol 

Permit your original yeast mixture to stand in a warm place for 
several days until signs of fermentation have about ceased. Now, 
taste the mixture to see if you can detect the sharp sting and the 
sweet taste of alcohol. Place the mixture in a distilling flask and 
distill the alcohol as in Ex. 17, Art. 24. What is the first of the 
distillate? Do you secure enough alcohol vapor to burn? 



298. Yeasts and Fermentation. — All the practical uses 
which we make of yeasts center in the peculiar relation which 
they bear to sugar. In the first place, sugar seems to be their 
natural food. It has been found possible to grow them in 
certain mixtures which do not contain sugar but in all the 
practical processes in which we use them, a sugar solution of 
some kind is used as a culture, or material in which to 
grow them. 

Under certain conditions it is known that yeasts use sugar 
as food, digesting, absorbing and assimilating it just as ani- 
mals do. Under other conditions, especially in the absence 
of oxygen and in an excess of sugar, the yeast digests and 
absorbs the sugar. But when it is taken into the body of the 



272 MICROORGANISMS 

yeast plant it is probably acted upon by an enzyme which 
merely breaks the sugar molecules up into molecules of alcohol 
and carbon dioxid. The alcohol and carbon dioxid is then 
thrown off from the yeast plant into the culture medium. 

This process of breaking sugar up into alcohol and carbon 
dioxid by the yeast plant is entirely distinct from the use of 
sugar as food by the yeast plant. It is, and always has been, 
something of a mystery as to what benefit the yeast plant de- 
rives from the process. Possibly the yeast plant gets a little 
energy from the process, if so, it is very little; perhaps the 
process is Nature's way of affording protection to the yeast 
plant, for up to a certain concentration, the alcohol does pre- 
vent the growth of other organisms, but is not detrimental to 
the yeast; possibly the process is of no material benefit to the 
yeast plant at all. 

299. Yeasts and the Production of Alcoholic Liquors. — 
All intoxicating liquors derive the alcohol they contain from 
the process of alcoholic fermentation carried on by yeasts. In 
the making of all the different kinds of liquors, a sugary solu- 
tion of some kind is always provided. This is inoculated 
with a quantity of yeast and kept at a suitable temperature 
until the fermentation has gone as far as desired, or until the 
accumulating alcohol has killed the yeast and stopped the 
process. 

In the case of wines, beer, and ale, the mixture is next put 
into bottles or kegs and is ready for use. In some of these 
undistilled liquors, the bottling is done before fermentation 
has entirely ceased, and thus a considerable quantity of car- 
bon dioxid remains in the liquor. This adds to the flavor of the 
liquor and is responsible for its sparkling quality. The color 
and part of the flavor of wines is derived from the fruit 
juices used in making them. 

In the making of distilled liquors, such as whiskey, rum, 
and brandy, the process of fermentation is carried as far as 
possible and then some of the water of the mixture is removed 
by the process of distillation (see Art. 24). 



SAPROPHYTES 273 

In making liquors from cereals, such as corn, rye, and bar- 
ley, -the starch of the cereal is first changed to sugar by the 
process described in Art. 420, and then the sugar is fermented 
by yeasts. 

300. Yeasts and the Making of Bread. — It is the carbon 
dioxid which results from fermentation which is of use in 
making bread. The flour which is used in making bread con- 
tains some sugar and usually a little more sugar is added 
to the dough as it is mixed. The yeast that is mixed with 
the dough ferments this sugar and produces both alcohol and 
carbon dioxid. The flour also contains a considerable quan- 
tity of a protein substance, gluten (Art. 413). The gluten 
gives the dough its sticky character and makes it more or less 
impervious to gases. Consequently, as the yeast produces 
carbon dioxid throughout the dough, the gas collects and 
forms little cavities in the dough making it light and porous. 
You have seen (Art. 12) that alcohol is a very volatile sub- 
stance. Consequently, in baking the bread, all the alcohol is 
vaporized. As the bread is baked, the gluten of the dough 
is so changed in character as to become quite porous to gases. 
It, therefore, allows both the vaporized alcohol and the carbon 
dioxid to escape. 

You thus see that we use yeast in making .bread, primarily, 
for a sort of mechanical effect which it produces on the bread, 
making it light and porous, and on this account more easily 
digested. In addition to this, the yeast adds a nut-like flavor 
to the bread which we like very much. 

If the knowledge of the role that yeast plays in bread 
making is of any practical value, it lies in the fact that the 
bread maker will realize that she is dealing with living or- 
ganisms. If she has this fact in mind, she is likely to be more 
intelligent in providing favorable conditions for the growth 
of the yeast. In general, it may be said that the best bread 
results from a moderately rapid fermentation, but the details 
of managing yeast for bread making are too numerous for us 
to enter into here. 



274 MICROORGANISMS 

301. Wild and Cultivated Yeasts. — All the different kinds 
of yeast used in bread making, except that used in making 
salt rising bread, and all that are used in the breweries and 
distilleries, are what may be called cultivated yeasts. These 
consist of several distinct species and varieties which vary in 
their usefulness for different purposes. All have been in use 
by man for so long a time that their origin from the wild state 
cannot be traced. In addition to these, wild yeasts of several 
kinds are widely distributed in the soil and air and it is these 
that are used in fermenting fruit juices in making wines. 

Exercise 66. — Study of Wild Yeast 

Place a little fresh apple cider or other available unfermented 
fruit juice in a glass tumbler and allow it to stand in a warm place 
for several days. After the fruit juice has shown signs of fermenta- 
tion, mount a drop of it on a microscope slide and examine it under 
the high power of the microscope for yeasts. You will probably 
be able to notice that the yeast cells differ in shape somewhat from 
"the tame yeasts that you formerly studied. 

302. Yeasts and the Preservation of Foods. — Wild yeasts 
are floating everywhere in the air. They are constantly 
falling into our foods. They are consequently always coming 
into competition with us for our sugar-bearing foods. Such 
foods as apple sauce, fruits of all kinds, and other sugar-con- 
taining foods are always in danger of being fermented by 
wild yeasts. We protect them somewhat by keeping them at 
low temperature in a refrigerator and sometimes in other 
ways. 

It is a rather peculiar fact that some foods which contain 
much sugar are seldom attacked by yeasts. This is true of 
syrups, rich preserves, and jellies. While sugar is the princi- 
pal food of yeasts, strong concentrations of it serve as a pre^ 
Tentative against both yeasts and bacteria. When yeasts and 
bacteria fall into strong concentrations of sugar, so much 
water is drawn from their bodies by the sugar that they are 
Jailed. This does not occur in weak solutions of sugar. 

This fact is sometimes used in the home treatment of 



SAPROPHYTES 



275 



wounds. Bacteria can be prevented from getting into an 
open wound by pouring a considerable quantity of granulated 
sugar on to the wound just before it stops bleeding. The 
sugar makes a thick syrup with the blood. This syrup will 
usually kill all bacteria which would otherwise enter the 
wound. If the wound is then wrapped up and kept clean it 
usually will heal without the least inflammation. 





Fig. 196. — Louis Pasteur. 



Fig. 197.— Robert Koch. 



BACTERIA 
We have seen that molds and yeasts are rather important 
factors in our environment. In some ways they render us 
important service and in other ways they are the cause of 
great inconvenience to us. Bacteria are of tremendously 
greater importance to us in both these ways than are either 
molds or yeasts. Bacteria are the smallest of living things and 
they are doubtless the most widespread in their distribution. 
We might well consider ourselves fortunate that we are living 
in these days since the perfection of the microscope which 
has enabled men to learn something of this teeming invisible 
world of life which touches us on every hand. 



276 MICROORGANISMS 

303. Development of the Science of Bacteriology. — The 

first authentic report which we have of bacteria having been 
seen by man was in 1683. Anthony Van Leeuwenhoek, a 
Dutch linen weaver, who spent his leisure time in grinding 
lenses and in using them to study various materials, was the 
first man to see and to describe these wonderful little living 
creatures (minute plants, not animals) which you are soon 
to have the privilege of seeing. In a letter to the Royal So- 
ciety of London, he said : "I saw with wonder that my material 
contained many tiny animals which moved about in a most 
amusing fashion. ' ' Are you going to see these organisms for 
the first time "with wonder," or are you going to consider 
it a commonplace experience just as we do many wonderful 
things in these days? Very little progress was made in the 
study of bacteria for nearly two centuries after Leeuwenhoek 's 
discovery. It was not until the latter half of the nineteenth 
century that the science of bacteriology had its wonderful 
development. This development of a science from the faint- 
est beginnings to one that ranks in the very forefront of the 
various branches of knowledge within the time of a single 
generation, was very largely due to the work of two great men. 
These men are Louis Pasteur (Fig. 196) who may be called 
the father of bacteriology and Robert Koch (Fig. 197) who 
may be said to be the man who made bacteriology an inde- 
pendent science. You should improve the first opportunity 
to learn something of the personal lives and of the work 
of these men. 

Exercise 67. — Study of a Hay Culture 

Fill a large glass jar with water, preferably water from some 
pond or stagnant pool, and put a good sized handful of timothy 
hay into the water. The hay should be cut into small pieces before 
it is put into the water. Place the jar in a warm place and continue 
to study the organisms that appear in it for several days. If the 
temperature of the water does not fall below 70° F. you should find 
it teeming with bacteria at the end of 24 or 48 hours. Bacteria 
will continue to be abundant in the culture for several weeks. If 



SAPROPHYTES 277 

you study a sample of the water about every other day for a period 
of two or three weeks, you will find that different forms of bacteria 
will be most abundant at different times. If the jar is allowed to 
stand for a month or two, all bacterial action will finally cease and 
the water will become quite clear. Can you suggest the reason 
for this? 

304. Life History of a Hay Culture. — Along with the dif- 
ferent kinds of bacteria -which from time to time will appear 
in the culture, you will find a great many different kinds of 
microscopic animals. As you study the culture from time to 
time, you will find that each kind of animal, like each kind 
of bacterium, will seem to have its day and then gradually 
disappear to give place to some other form. The reason for 
this shifting panorama of life which a culture like this exhibits 
is found in the varying chemical conditions of the culture 
which are brought about by the organisms themselves. Thus, 
a given organism becomes the leading type whenever the con- 
ditions of the culture are most favorable for it. This type of 
organism gradually consumes the food available to it and at 
the same time contributes harmful waste materials to the 
culture. When this continues for a time, the conditions of the 
culture become gradual^ more unfavorable for this particu- 
lar form, but at the same time it becomes more favorable for 
a succeeding form of life. This succeeding form then be- 
comes the leading type in the culture for a time and then, in 
its turn, in the same way, and for the same reasons, gives way 
to a new successor. 

Now, if you can imagine, not one line of succession like this, 
but many such lines going on at the same time, you will have 
a fairly accurate picture of what is going on in your culture. 
Not only this, but this picture of change in your- culture is a 
fairly accurate picture of what is going on in nature every- 
where. 

The story is thus : Green plants feed upon the simple inor- 
ganic compounds found in the soil, air and water. They 
build these into complex compounds of organic matter within 



278 MICROORGANISMS 

their bodies. They die. Bacteria feed upon the dead bodies 
of these higher forms of life reducing the complex organic 
compounds again to simple inorganic compounds. These in 
turn become food for another generation of green plants. 
This is the ceaseless round of life and death. 

305. Decay in General. — It is a long and interesting story 
from the planting of an acorn to the final dissolution by natu- 
ral processes of the body of the giant oak that results. One 
might think that the story is ended when the tree has come 
to its death, but with this picture of your culture in mind 
you will see that probably the most interesting part of the 
story begins with the death of the tree. Thousands of dif- 
ferent forms of life take part in its destruction. It is in this 
work of the dissolution of organic bodies that microorgan- 
isms play their most important role in the life of the earth. 

Fig. 198. — Cocci, spirilla, and bacilli. 

Were it not for the work that these organisms do, the earth 
would become strewn with the dead bodies of animals and 
plants, and the chemical elements which composed these bodies 
would never again become available for succeeding forms 
of life. 

306. Forms of Bacteria. — As you study your culture from 
time to time, you will have opportunity to observe the three 
different forms of bacteria (Fig. 198, A, B, C). Sometimes 
you will have all three forms on your slide at once. The three 
forms are: first, spheres, called cocci (pronounced coc-sal), 
(singular, coccus), A; second, rods called bacilli (singular, 
bacillus), B; spirals called spirilla (singular, spirillus), C. 
Some of each of these forms have swimming organs, thread- 
like appendages, B, and these are able to swim through water. 
Most of them lack these organs and are, therefore, non-motile, 



SAPROPHYTES 27$ 

or without the power of self-motion. The bacilli are most 
numerous, the cocci rank next, and the spirilla are least 
numerous. Migula, the German bacteriologist, in 1900 de- 
scribed 833 different bacilli, 343 different cocci, and 96 dif- 
ferent spirilla. 

It is a most difficult task to distinguish these different kinds 
of bacteria. Two different bacteria may look for all the world 
alike under the microscope, and yet the waste products they 
produce may be very different. These products from one may 
be a violent poison in our bodies while the products from the 
other may be perfectly harmless to us. 

307. Where Bacteria May Be Found. — It would be easier 
to say where bacteria are not found for they are found 
almost everywhere. They are doubtless absent in the midst 
of deserts, in the depths of the sea, in the frigid regions 
near the poles, and in the tissues of healthy animals and 
plants, but in almost any other place on or near the surface 
of the earth they are present in great abundance. Bacteria 
are ever present in the soil, water, and air, in the food and, 
consequently, in the mouths and alimentary tracts of animals, 
and in all decaying organic substances everywhere. 

They are never growing and active, however, unless they 
are supplied with an abundance of water, a suitable food 
supply, and a favorable temperature. In the ordinary form, 
they can endure drouth and remain alive for some time; the 
different kinds vary greatly in this power, however. Some 
kinds have the power of forming spores which endure drying 
for many months, some even for many years, and still retain 
the power of growing whenever they fall into suitable condi- 
tions. In the formation of these spores, the whole living 
part of a bacterium contracts into a spherical body within the 
original cell wall; a new and thicker wall is secreted about 
this body; the original wall bursts and the spore is set free. 
The spore is thus a means of living over an unfavorable sea- 
son, or of resting until suitable conditions for growth return. 
The fact that bacteria are able to endure drought either in 



#80 MICROORGANISMS 

the spore form or in the ordinary form, accounts for their 
wide distribution and for the fact that they are present and 
ready to begin active growth whenever and wherever any 
suitable material is found for them to grow in. 

1. Soil Bacteria 

308. Study of Soil Bacteria. — 

Exercise 68. — Soil Bacteria 

Procure some rich soil from a stable lot or a garden. Fill a glass 
tumbler half full with the soil and then fill the tumbler to the top 
with water. Stir the mixture thoroughly and allow it to settle. 
After the soil has settled, examine a drop of the water under the 
high power of the microscope for bacteria. Examine a drop of 
clean well water in the same way and compare the number of bacteria 
in the two samples of water. 

You will get the idea from this experiment that the soil 
contains myriads of bacteria. In the water taken from the 
tumbler containing the soil, you will doubtless find some mi- 
croscopic animals similar to those you found in your hay cul- 
ture. The two kinds of organisms in the soil bear the same 
relations to each other as they do in the hay culture. That is, 
the bacteria of the soil feed on the dead organic matter of the 
soil, and the microscopic animals in turn feed on the bacteria. 

309. The Nature of Soil. — Before taking up the relation of 
bacteria to the soil, it is necessary for us to know something 
of the nature of soil. Geologists tell us that the outer crust 
of the earth was originally solid rock, and that through the 
influence of weathering agencies, such as the sun and wind, 
freezing and thawing, and the flowing of water, much of this 
crust of rock has been ground into exceedingly fine particles. 
These fine particles now make up a deep layer of soft material 
which we know as clay, sand, and gravel and which covers the 
deeper solid rock of the earth's crust. For a few inches or 
feet below the surface, this clay and sand and gravel is, in 
most places, well mixed with decaying remnants of the bodies 



SAPROPHYTES 281 

of plants and animals. It is these few inches or feet on the 
surface of the soft blanket of the earth that are well mixed 
with organic matter that we call soil. It is in this thin layer 
of soil, mainly, that the materials are contained which the 
higher plants take in through their roots and use in building 
up the more complex foods with which they nourish them- 
selves and the rest of the living world. The organic matter in 
the soil is collectively spoken of as humus and it is this humus 
which supplies food to the soil bacteria. 

310. Soil Bacteria and Carbon. — The soil bacteria complete 
the work of destruction of the particles of plant and animal 
matter which fall into the soil. All these materials contain 
large quantities of carbon combined with other chemical ele- 
ments and when the bacteria have digested, absorbed, assimi- 
lated, and respired them, the carbon escapes to the air in the 
form of carbon dioxid gas. This you will remember is the 
form in which the green plants take up carbon from the air 
and again combine it in a form which serves as food. Thus it 
is that bacteria, and other agents, such as other non-green 
plants and animals keep constantly returning carbon dioxid 
to the air where it becomes available for the green plants. 

311. Soil Bacteria and Nitrogen. — We shall see in Chap. 
VII, Art. 370, that only a comparatively small number of 
chemical elements are needed to make up the numerous 
chemical compounds that constitute the human body. This 
is true of all living bodies. Among these few necessary ele- 
ments there is none that gives us greater concern than nitro- 
gen. This element constitutes about four-fifths of the atmos- 
phere, but it is not found in a combined form in the natural 
rock of the earth. It is therefore not in the soil in a com- 
bined state except as it has been put there by living organ* 
isms. 1 On this account, the nitrogen supply of the soil is 

1 Xote : Small amounts of combined nitrogen are carried down by 
rain during storms, especially thunder showers. Lightning causes some 
of the nitrogen and oxygen of the atmosphere to unite into chemical 
compounds, gases, which are absorbed by the falling rain. 



282 MICROORGANISMS 

usually more limited than that of the other soil elements 
which were present in the original rock of the earth from 
which the soil was made. At the same time no living thing 
can exist without nitrogen for it is one of the necessary 
elements in the makeup of protoplasm. 

The green plants take up the nitrogen from the soil in cer- 
tain definite chemical compounds, usually in the form of 
nitrates, such as potassium nitrate. The green plant has 
the power of combining the nitrogen in this form with other 
elements to form proteins (Art. 384). These proteins are 
food for the green plant and for other organisms. The nitro- 
gen which is thus formed into protein compounds by green 
plants is practically the only available supply of nitrogen for 
the animal world. Animals do not have the power of making 
proteins out of nitrates or other similar compounds. We get 
proteins when we eat the flesh of other animals, but this, in 
turn, may always be traced back to proteins formed by some 
green plant (see Art. 374). 

312. Some Qlasses of Soil Bacteria. — Now, it is probably 
evident to you why we are so greatly concerned about the 
supply of nitrogen in the soil in a form available to the green 
plants. With this thought in mind, you will doubtless be 
interested to know the part that the soil bacteria play in keep- 
ing up this supply of available nitrogen in the soil. The 
bacteria which do this work may conveniently be divided into 
three groups: (1) The nitrifying bacteria, (2) the nitrogen 
fixing bacteria, and (3) the nodule bacteria. 

313. The Nitrifying Bacteria. — The nitrifying bacteria 
transform the various nitrogen-bearing compounds of the soil 
humus into the nitrate form. This is not a simple process, 
as you might suppose, but consists of three distinct steps. 
Each step in the process is performed by a different set of 
bacteria, but several different species of bacteria are known 
for each step. 

The first step in the process is the changing of the proteins 
and other nitrogen-bearing compounds of the humus into 



SAPKOPHYTES 283 

ammonia. If you turn over a rapidly decaying mass of 
organic matter, you can usually detect the characteristic odor 
of ammonia along with various other odors. 

The second step in the process is carried on by an entirely 
different set of bacteria and results in changing the ammonia 
to nitrites. Nitrites differ, chemically, from nitrates in 
having relatively less oxygen in their composition. 

The process is completed by another set of bacteria which 
changes the nitrites to nitrates. 

It is evident that these bacteria which simply transform 
the nitrogen-bearing compounds of the soil humus into a form 
available for the higher plants do not actually add any nitro- 
gen to the soil. They only transform nitrogen that is already 
there. If you recall the fact (Art. 311) that the original rock 
of the earth does not contain any fixed nitrogen, you will see 
that we so far, have no means of accounting for the origin of 
the present nitrogen content of the soil. The bacteria of this 
group only aid in keeping the nitrogen in circulation, they do 
not add to the total stock. 

314. Nitrogen Fixing Bacteria. — A second group of bac- 
teria which have to do with the nitrogen content of the soil 
consists of several species which recently have been discovered 
and proved to be able to take the free atmospheric nitrogen 
and fix it in compounds which finally become available for 
the higher plants. These bacteria live in the soil and derive 
their carbo-hydrate food from the humus just as others do. If 
fixed nitrogen, i.e., nitrogen in the form of nitrogen com- 
pounds, is abundant in the soil, they also use this. In the 
case, however, of the scarcity or absence of fixed nitrogen, 
they are able to draw on the great ocean of free atmospheric 
nitrogen. Unlike the first group discussed above, these bac- 
teria are thus able to add to the total nitrogen content of 
the soil. It is doubtless true that these organisms have been 
important factors in bringing about the gradual increase in 
the nitrogen content of the soil that ha,s occurred during the 
ages. 



284 MICROORGANISMS 

In ancient times the custom of fallowing land was largely 
practised. This consists of cultivating the land for a season 
to keep down the weeds without attempting to raise a crop 
on it. It was believed by the ancients that in some way 
through this practice, the land was enabled to produce a very 
much better crop the following season, and this belief was 
abundantly supported by practical experience. We now have,- 
at least, a partial explanation of this fact in these bacteria 
which add atmospheric nitrogen to the soil. 

315. Nodule Bacteria. — The third group of bacteria that 
affect the nitrogen of the soil, like the second group, have the 
power of fixing atmospheric nitrogen but they seem to be able 
to do this only when they live within the root tissue of certain 
higher plants, mainly those that belong to the botanical family 
which includes clover, alfalfa, beans, peas, and the like. 
When these organisms grow in the roots of the host plant, they 
cause little outgrowths, or knots, to form on the roots, which 
are called nodules, and the bacteria themselves are often 
spoken of as nodule bacteria (Fig. 199). The nitrogen in 
the soil air is taken in by these nodule bacteria and combined 
with other chemical elements. The new materials thus formed 
become available food for the host plant. When the host plant 
finally dies and decays, the nitrogen fixed by the nodule bac- 
teria becomes a part of the soil. 

It has long been known by practical farmers that plants 
belonging to the clover family tend to increase the produc- 
tivity of the soil. It is only recently, however, that the dis- 
covery was made that it was not the higher plant, the clover, 
itself, that was the cause of the increase in the nitrogen con- 
tent of the soil but that it was the work of the nodule bac- 
teria. 

316. Summary of the Work of Soil Bacteria. — There are 
three groups of soil bacteria which tend to increase the nitro- 
gen content of the soil: 1. Nitrifying bacteria; 2. Nitrogen 
fixing bacteria ; and 3. Nodule bacteria. 

The first group, nitrifying bacteria, are merely the active 



SAPROPHYTES 



285 




Fig. 199— Roots of red clover (above) and of soy bean (below), show- 
ing nodules formed by nodule bacteria. 



286 MICROORGANISMS 

ag'ents which return to the soil the nitrogen which has been a 
part of the bodies of higher forms of life. Nitrifying bacteria 
do not in any way add to the total amount of nitrogen in the 
soil and in the bodies of the higher forms of life. They merely 
keep the nitrogen in circulation. We shall study them fur- 
ther under the head of decay. 

The other two groups, nitrogen fixing and nodule bacteria, 
actually seize upon atmospheric nitrogen and so combine it 
with other elements that it becomes available as food for the 
green plants. 

317. Effect of Cropping on Soil Nitrogen. — In a state of 
wild nature, in which all plants which grow upon the soil, 
die where they stand and soon decay, returning their nitrogen 
to the soil, there is a gradual but constant increase in soil 
nitrogen. This should mean a gradual increase in the fer- 
tility of the soil. This increase in fertility of soil should 
mean a gradual increase in the luxuriance in plant growth. 
This, in general, we believe has been the history of the 
world. 

Under the usual methods of agriculture, however, a large 
portion of the crops grown on the land is often removed. As 
a natural result we should expect that the soil nitrogen, and 
therefore the fertility of the land is reduced. If the amount 
of nitrogen carried away in the crops removed, together with 
the nitrogen which is carried off with the drainage, is greater 
than the amount of nitrogen which is added to the soil by the 
soil bacteria and manures and fertilizers which may be added, 
there must be a decrease in the amount of nitrogen which re- 
mains in the soil year after year. 

If the practice of removing more nitrogen from the soil than 
is added to it is kept up for many years, the soil becomes ever 
poorer and poorer and in the end will become so unproductive 
that it no longer pays man to till it. This thing has actually 
happened in the case of many originally fertile soils of the 
world. All the older states of this relatively new country 
contain abandoned farms. These farms have become so ex- 



SAPROPHYTES 287 

hausted of nitrogen, and probably of other necessary elements, 
that they no longer produce crops which pay. The owners 
have ceased to till them. 

318. Interrelations of Soil Bacteria. — In this account of the 
relation of bacteria to soil fertility, we have given only the 
mere thread of the story. Many interesting interrelations 
exist between the different kinds of soil bacteria which our 
limited space will not permit us to consider. 

Some different kinds of bacteria are helpful to one another. 
In some cases they are almost powerless to carry on their 
processes without this mutual aid. In other cases, different 
kinds seriously interfere with one another, not only com- 
peting for food, but through their wastes and secretions 
hindering one another's development. Some even undo the 
work that others do. For example, there are great numbers 
of bacteria in barnyard manure and some of them in the soil 
generally that have the power of breaking up the nitrates of 
the soil and setting the nitrogen free in the atmosphere. 
These are called denitrifying bacteria and they tend to undo 
the work accomplished by the three groups discussed above. 

Some of the soil bacteria must have free gaseous oxygen 
supplied them for respiratory purposes, while others can not 
only get along without free oxygen, but can not carry on their 
processes in its presence. These latter obtain the oxygen 
which they use in respiration from chemical compounds which 
contain it. The kinds of bacteria that must have free oxygen 
are known as aerobic bacteria; those that do not require 
it are known as anaerobic bacteria (See Chap. X, Sec. V). 

Many other details like these are known to bacteriologists 
and doubtless there are very many more important relations 
that exist among these organisms and between them and 
their environment which have not yet been discovered. 
Furthermore, other soil elements are affected by bacteria in 
ways very similar to those in which nitrogen is affected, and 
numerous complex relations exist among these different 



288 MICROORGANISMS 

soil elements and among the organisms that affect them. 
Thus you see that the soil is not the dead, inert, and un- 
changing thing that you might suppose it to be. It is teem- 
ing with life and endless change. It presents an endless list 
of problems to man for solution and as fast as man is able 
to solve these problems, he is able to deal with the soil more 
intelligently. Our knowledge at present is very incomplete 
but it is sufficient to enable us greatly to increase the produc- 
tivity of the soil if the men who till the soil only knew and 
practised what is known to men of science. 

2. Bacteria and Decay 

319. Real Meaning of Decay. — So far, we have considered 
bacteria mainly from the standpoint of the services they ren- 
der us and the rest of the living world, by keeping up the 
fertility of the soil and by helping to keep in circulation the 
chemical elements which living organisms need. "We shall now 
change our point of view, for a time, and consider how they 
tend to destroy many things which we wish to preserve. 

The disintegration of organic materials through the agency 
of bacteria or other fungi is commonly spoken of as decay, 
rotting, spoiling, or putrefaction. These different terms 
came into use before the real nature of the process referred to 
was recognized and they are still used to some extent, though 
more or less vaguely, to represent different forms of the 
process. Thus, for example, when disagreeable odors result 
from the process, as often occurs in the disintegration of pro- 
teins, the process is often spoken of as putrefaction. All of 
these terms really mean the same thing; they are different 
names for a single process by which the nature of matter is 
changed. They are different terms applied to the chemical 
changes brought about by microorganisms. Hence, we shall 
use the single word decay to represent the process in all 
its forms. 

Doubtless, you have already recognized the disintegration 
of the soil humus as decay. In this instance, we are inter- 



SAPROPHYTES 289 

ested to have the decay go forward at a rate sufficiently rapid 
to supply our growing crops with an abundance of mineral 
salts. So it is with many things that are useless to us; we- 
are quite willing that they shall be disintegrated and not 
allowed to encumber the earth (see Sewage Disposal, Chap. 
X). There are many other things, such as our food, clothing,, 
and lumber which we wish to preserve and which the bacte- 
ria and other fungi stand ready to consume. 

3. Conditions Which Favor Bacterial Growth 

320. Warding off Attacks of Bacteria. — We can ward off 
the attacks of bacteria by so conditioning the material which 
we wish to preserve that bacteria can not grow in it. In 
doing this, we need to know the conditions which favor bac- 
terial growth. These briefly stated are as follows: (1) a 
suitable food, (2) an abundance of water, (3) a favorable 
temperature, (4) suitable chemical conditions, (5) absence of 
bright light for most of them, (6) presence of free oxygen for 
some, and (7) absence of free oxygen for others. We shall 
consider these briefly in separate paragraphs. 

321. Food for Bacteria. — Bacteria can feed on a wide range 
of substances. Almost all organic compounds are food for 
one or more different kinds. Almost all species of bacteria 
can feed on protein substances and yet some can get along 
with no protein at all in their diet. Since the organic 
materials which we wish to preserve are almost always a mix- 
ture of many different kinds of compounds, we may be quite 
sure that any of these things of plant or animal origin are 
subject to the attacks of bacteria. 

322. Water Necessary for Bacterial Growth. — A mass of 
food material, in order to support an active growth of bacteria, 
must contain from 25 per cent, to 30 per cent, of water. This 
is considerably more water than is required to support a 
growth of mold. Many materials will be found to mold when 
they are entirely free from bacterial action. 

The high percentage of water required for bacterial growth 



290 MICROORGANISMS 

enables us to preserve many materials from their attacks by 
merely drying them. It is by drying out when ripe and 
remaining dry for long times that seeds of plants naturally 
avoid being consumed by bacteria during the resting period 
before germination. Many kinds of foods, such as fruits, 
vegetables, and the seeds of plants can be kept indefinitely by 
drying them out and keeping them dry. Building materials 
which are of plant origin, such as lumber, may be preserved 
indefinitely against the attacks of bacteria if they can be kept 
dry. We paint our houses largely for the purpose of making 
the lumber shed water and remain dry, and thus avoid the 
attacks of bacteria. 

323. Temperature Required. — Bacteria vary widely in their 
temperature relations. Some are able to grow at almost the 
freezing temperature, while others thrive at temperatures as 
high as from 160° to 190°F. Three temperature limits may 
be distinguished for each bacterium as follows: a minimum 
or the lowest temperature at which growth is possible; an 
optimum, or the temperature at which they grow best; and 
a maximum, or the highest temperature at which growth is 
possible. In some species the range between the minimum 
and maximum is wide, while in others it is comparatively 
narrow. The minimum temperature of some species is higher 
than the maximum of others. 

Considering this wide range of temperature relations, it 
is evident that it is very difficult entirely to prevent the action 
of bacteria, through the agency of temperature, in substances 
which are injured by freezing. At very low temperatures, 
just above the freezing point, very few bacteria are active and 
none are very active. This fact makes possible the preserva- 
tion of many kinds of food for comparatively long times by 
the method of cold storage (see Chap. VIII, Sec. III). 

324. Necessary Chemical Conditions. — Many chemical 
substances have been found to be detrimental to, or destruc- 
tive of, bacterial life. Most bacteria, for example, do not 



SAPROPHYTES 291 

thrive in acid media and on this fact rests the preserving 
power of vinegar and other organic acids. Common salt, salt- 
peter, and other similar materials nsed in preserving meats 
prevent the growth of bacteria but, in ordinary concentration, 
do not kill them. Such a substance is called an antiseptic. 
On the other hand, certain substances like corrosive subli- 
mate, carbolic acid, and formaldehyde, even used in compara- 
tively weak solutions, are deadly to bacteria. Such a sub- 
stance is called a disinfectant. 

325. Antiseptics. — Antiseptics of many kinds are widely 
used in the preservation of food. Common salt, vinegar, 
spices, and sugar are the ones most commonly used in the 
household. Sugar is a good food for some bacteria and par- 
ticularly so for yeasts and molds, but in very strong concen- 
tration such as is found in jellies, preserves, and the like, 
neither yeasts nor bacteria can grow. Molds, however, are 
more able to endure these strong concentrations of sugar. 
Boric acid is sometimes used in the preservation of meats and 
butter; formaldelr^de in the preservation of milk; and benzo- 
ate of soda, in the preservation of jams, catsups, and the like, 
but most authorities are agreed that these and several other 
substances like them are, in the long run, injurious to the 
health of the consumer and therefore their use is unwise. 

326. Disinfectants. — Disinfectants are used, not only for 
the destruction of bacteria in houses after a case of bacterial 
disease, but also in the preservation of lumber, railroad ties, 
fence posts, mine props, and the like. Among the disinfec- 
tants used for these latter purposes are creosote and zinc 
chloride. The material to be preserved is soaked in a solu- 
tion of the disinfectant and this prevents, not only the 
action of bacteria, but also the attacks of wood borers and 
other insects. 

327. Effect of Light upon Bacteria. — Most bacteria are 
readily killed by direct sunlight or other bright light. Even 
strong diffused light is highly detrimental to their growth. 



292 MICROORGANISMS 

This fact, however, is of little value in the preservation of 
materials, for the bacteria in the interior of the substances are 
effectively shielded from the light. 

328. Oxygen and Bacteria. — We have mentioned in Art. 
318, the fact that some bacteria require free oxygen in order 
to be able to carry on their processes, while others can not 
only get along without free oxygen, but can not thrive in its 
presence. The only importance that this fact has in con- 
nection with the preservation of food is that it shows that we 
can not hope to preserve the food by shutting it aw T ay from 
free oxygen. As far as the oxygen relation is concerned, 
the anaerobic bacteria find ideal conditions within a sealed 
can of fruit or vegetables, 

4. Preservation of Food by Canning 

329. Why We Can Food. — ¥e know that one of the most 
extensively used methods of preserving food at the present 
time is that of canning. This consists of putting the food 
into cans, heating it to a high temperature for a time suf- 
ficiently long to kill both the active growing bacteria and the 
more resistant spores, and then sealing it air-tight. 

Canning has been practised to some extent as a household 
industry for about a century, but the large canning factories 
which now preserve annually immense quantities of food 
have come into existence during the last 25 or 30 years. 
The importance of canning and other modern methods of 
preserving food as means of cheapening the cost of living is 
very great. Before these methods came into use, many kinds 
of food could be used only while it was fresh and in season, 
and a large percentage of each crop was allowed to go to 
waste for the lack of suitable methods for preserving it. Now, 
the whole crop may be saved and be sold at reasonable prices 
throughout the year. 

It is a remarkable fact, however, that, during the same 
period of time in which the process of canning and other 
methods of preserving food have been brought to their present 



SAPROPHYTES 293 

high state of development, the cost of food has greatly in- 
creased instead of decreasing. The increase in the cost of 
food has come about, however, in spite of the perfection of 
these processes which naturally have the opposite effect. 
Food would doubtless be much more expensive today than it is 
if we did not have these modern methods of preserving it. 

330. Domestic Canning. — As stated above, the canning of 
certain things, such as fruits and some of the vegetables, has 
been practised in the homes for a long time. This practice 
began long before the development of the science of bacteri- 
ology and, therefore, the reasons for the success of the methods 
used were not understood. The methods ordinarily used in 
the home are successful only with fruits and with certain vege- 
tables like tomatoes which contain a considerable quantity 
of acids. You will recall the fact that acids are generally 
detrimental to the growth of bacteria. It is doubtless on 
account of the influence of these acids that food, which con- 
tains them in sufficient quantities, may be canned successfully 
with the moderate degree of heat available in the ordinary 
household. 

It is difficult to heat food in the ordinary household to a 
temperature higher than that of boiling water. This tem- 
perature is not sufficient to kill, in a reasonable length of time, 
the resistant spores of certain bacteria which are always found 
on such foods as green corn, beans, and peas. Consequently 
these foods are seldom successfully canned in the home. 

There is a method, however, by which such foods may be 
successfully canned in the home without special apparatus. 
This consists in heating the food in the cans to the boiling 
temperature for about a half hour on each of three succes- 
sive days and then sealing up the cans with lids and rubbers 
which have also been heated along with the vegetables. The 
heating the first day kills all active growing bacteria and prob- 
ably serves to stimulate the spores to begin to grow. These 
then are killed with the second heating, and the third heating 
serves to kill any that may have escaped the first two heat- 



294 MICROORGANISMS 

ings. If the fuel and labor used in this process is expensive, 
it is likely that the food canned in this way will, in the end, 
cost as much as it would cost to buy the same amount of food 
which has been canned in a factory. 

331. Factory Canning. — As has been stated, the canning 
process as ordinarily carried on in the household, finds its 
limitations in the fact that the temperature of boiling water, 
the highest temperature conveniently obtainable without 
special apparatus, is not sufficiently high to kill the more 
resistant spores of molds and bacteria in a reasonable length 
of time. 

Canning factories, however, are equipped with special ap- 
paratus by means of which the food that is canned may be 
raised to any desired temperature. Such apparatus consists 
of what might be called a large steamer of boiler iron construc- 
tion. A large number of cans containing the food are placed 
in this steamer and then steam is turned into this apparatus 
until a certain pressure is reached. You are familiar with the 
fact that steam arising from boiling water is practically of 
the temperature of the boiling water; that when the steam is 
under 1 atmosphere of pressure its temperature is 100° C, 
or 212°F. ; but when steam is held under pressure, the tem- 
perature increases with the pressure. Consequently, by sur- 
rounding cans containing food with steam under pressure, 
the food may be raised to a temperature sufficiently high to 
kill in a few minutes the most resistant spores of micro- 
organisms. 

When the cans # are placed in the heating apparatus, they 
are generally sealed up except for a very small hole in the 
top of the can. As soon as the cans come from the heating 
apparatus, a drop of solder is dropped on this hole and it is 
sealed. This hole is left in the can while it is being heated 
for the purpose of permitting the air which is contained in the 
can to escape as it is expanded by the heat. Since the hole 
is sealed up while the contents of the can are still very hot, 



SAPROPHYTES 295 

and therefore more or less expanded, the contents of the can 
will shrink slightly on cooling and the ends of the can will 
become slightly concave or sprung in, as a result of the at- 
mospheric pressure on the outside. This fact is important 
as it affords a means of detecting cans which have not been 
perfectly preserved. Some kinds of bacteria are gas pro- 
ducers and when they begin action on the food in a can, they 
soon set free sufficient gas to cause the ends of the can to 
bulge out and become convex. Cans which thus show this 
swelling are discarded before they leave the factory. Some 
kinds of bacteria, however, do not produce gases by their ac- 
tion and so the failure of a can to swell is not an absolute 
guarantee that the food is perfectly preserved. 

In ordinary practise in canning factories, the food is heated 
to a temperature of from 110°C. to 125°C. for from 20 
minutes to a half hour. The time and temperature vary with 
the kind of food that is being preserved and with the size of 
the cans. Equipped with this power to destroy by heat the 
most resistant forms of microorganisms, the canning factories 
are able to preserve any kind of food that is not seriously 
injured by the high temperatures. Fruits and vegetables of 
every kind, milk, meats, soups, and many other forms of food 
prepared ready for use are now preserved by canning. 

These foods are preserved when they are in season and, 
generally, in the part of the country where they are produced. 
They then become available throughout the year and in every 
part of the country. Before the introduction of canning, the 
food of the people naturally varied considerably at different 
times of the year. Fruits and vegetables were abundant in 
the summer time and scarce in the winter. Now we may have 
practically the same variety of foods throughout the year at 
very little added cost. 

Canning factories, like most other modern factories, have 
many forms of labor-saving machinery which help to cheapen 
the cost of their products. A discussion of these, however, 



296 MICROORGANISM'S 

would take us outside our present topic, and besides this, you 
could learn more in an hour's visit to a neighboring factory 
than we could tell you in several pages. 

332. Sterilization "and Pasteurization. — It is evident from 
the foregoing that the process of canning depends on the com- 
plete destruction of all forms of living organisms in the food. 
The process of killing all microorganisms in a given substance 
is known as sterilization. 

Most of moist foods are favorable foods for bacteria to 
thrive in. If such foods are to be kept for any considerable 
time, they must be completely sterilized and thoroughly sealed 
from bacteria. If a single living bacterium or a single living 
spore is left in the food, it will soon multiply and the food will 
be destroyed. 

Many times, however, we care to preserve food for only a 
short time. In such cases complete sterilization is not neces- 
sary. Furthermore, some foods, like milk, are seriously in- 
jured by the high temperature necessary for complete steril- 
ization. 

If milk is heated even to boiling, some of the proteins 
which it contains are coagulated and the flavor of the milk is 
greatly changed. The coagulated protein is not so easily 
digested as it is in the fresh state and the changed flavor 
makes it less palatable than fresh milk. Consequently, since 
milk is usually consumed within 24 to 48 hours after it is 
drawn from the cow, the bacterial action which might other- 
wise cause it to sour within that time may be effectively 
prevented by heating the milk after it is bottled to a tem- 
perature sufficiently high to kill only the active growing bac- 
teria which it contains. If milk is heated to 60°C, or 140°F., 
for 20 minutes, all the active bacteria in it will be killed, but 
the milk will not be changed essentially in flavor or digesti- 
bility. Such an amount of heating is not sufficient to kill the 
bacterial spores in the milk and these will soon begin to grow 
and multiply and the milk will finally sour. The souring 
is delayed by this process, however, and this delay usually 



PARASITES 297 

makes it possible for the milk to be delivered to the consumer 
and consumed before the souring occurs. 

This process of heating food to a temperature sufficiently 
high and for long enough time to kill the active bacteria but 
not to kill the spores, is called pasteurization. You will note 
by the spelling of the term that it is named for Pasteur (see 
Art. 303). Pasteur did not originate the process, but he per- 
fected it and applied it in several practical ways and suc- 
ceeded in inducing people to make use of it. 

333. Pasteurization and the Spread of Disease. — This de- 
lay in the souring of milk is by no means the most important 
result of the practice of pasteurizating milk. A far more im- 
portant result lies in the fact that disease-causing bacteria 
which the milk may chance to contain are effectively killed by 
the process. Milk is an ideal food for most bacteria and, for 
this reason, it often becomes a means for the spread of 
bacterial diseases, such as typhoid fever, tuberculosis, and 
diphtheria. Xone of the bacteria which cause the more com- 
mon contagious diseases are known to form spores and, there- 
fore, any such bacteria are effectively killed by pasteurization. 

II. PARASITES— ORGANISMS WHICH LIVE WITHIN' THE 
BODIES OF OTHER LIVING ORGANISMS 

334. Parasites and Their Hosts. — You will recall the state- 
ment made in Art. 287 that organisms which live and find 
their food within the bodies of other organisms are known 
as parasites. The organism within whose body a parasite 
lives is known as the host. Parasites often produce certain 
poisons, or toxixs, in the body of the host. These poisons 
attack certain parts of the body of the host and thus the para- 
sites become the cause of what we commonly call diseases. 

The larger animals are affected by many kinds of animal 
parasites, such as tapeworms, trachina, and the malarial 
parasite, but most of the common diseases are caused by plant 
parasites and the bacteria are by far the worst offenders in 
this way. A good many different kinds of bacteria, how- 



298 MICROORGANISMS 

ever, are known to live and thrive within the months and 
alimentary tracts of man and of other animals which are not 
known to cause any harm to their hosts. Indeed, it is thought 
by some bacteriologists that some of these bacteria are of 
benefit to their hosts in some unknown way. 

335. Former Theories of Disease. — Before taking up a dis- 
cussion of the nature of bacterial diseases, it might be well to 
consider briefly some of the early theories that have been 
held concerning the cause of disease. One of the earliest of 
these theories consisted in a belief that the diseases were 
caused by an "evil spirit" which entered into the body and 
behaved in such a manner as to bring pain and suffering to 
the patient. Such a theory was more or less of a natural 
inference from a superficial study of the symptoms of an 
ordinary disease. This theory seems to have fitted particu- 
larly well as an explanation of diseases accompanied by high 
fevers and a delirious condition and in cases of insanity. 
This theory was held longest in regard to diseases of this 
type. 

Two different lines of treatment were followed in attempt- 
ing to cure diseases according to this theory. It was thought 
that the spirit could either be coaxed to leave the body of 
the patient by sacrifices or promises, or it could be forced to 
leave by charms, by the beating of tom-toms, or by torturing 
the body of the patient, and thus making it uncomfortable for 
the intruder. You have doubtless read of some of the strange 
customs practised by savage tribes today in the treatment 
of their sick. Most of such customs grow out of some form of 
this theory of disease, for it seems that most present-day 
primitive peoples, as well as the savage ancestors of civilized 
man, hold to this theory in some form. 

336. Semi-scientific Theory of Disease. — Hippocrates, a 
Greek philosopher, who was born about 460 B. C. and who is 
often called the "Father of Medicine," announced a new 
and semi-scientific theory of disease. According to this 
celebrated theory, the body contains four humors: blood, 



PARASITES 299 

phlegm, yellow bile, and black bile. Health consisted of a 
proper mixture of these four humors and disease consisted of 
an improper mixture. The treatment of diseases according 
to this theory, consisted in an effort to keep the humors in a 
proper relation to one another. This was done by administer- 
ing powerful drugs. This theory soon gained world wide 
acceptance and it was the theory of disease generally accepted 
throughout the whole of the dark ages. Indeed, its influence 
is still seen in much of the current thought and practice in 
medicine. By the giving of drugs of many kinds for many 
kinds of diseases, a large number of really valuable medicines 
which are in wide use today were thus empirically discovered, 
i.e., discovered by experiment. Quinine, for example, was 
known to be a cure for malaria long before it was known 
that the disease is caused by a little microscopic animal which 
is killed by the quinine. 

It must be some little" surprise to you to realize that it was 
not until a comparatively recent date, when the germ theory 
of disease began to be generally accepted, that the practice 
of medicine really began to be placed on a sound scientific 
basis. The year 1876 is a memorable year in the history of 
medicine. It was in that year that Robert Koch succeeded 
in proving beyond the possibility of a doubt that a certain 
disease of domestic animals was caused directly by a certain 
rod-shaped bacterium which is now known as bacillus an- 
thrax. Since this is a typical bacterial disease and one 
about which a great deal is known, we shall use it to illustrate 
the nature of a bacterial disease. 

1. Anthrax 

337. Animals Affected. — Anthrax, or splenic fever, as it 
is sometimes called, is, in nature, primarily a disease of cattle 
and sheep though it sometimes attacks a large number of 
other animals including man. Horses, hogs and dogs have a 
relatively high degree of resistance to the disease though none 
of them are entirely free from occasional attacks of it. Rab- 



300 



MICROORGANISMS 



bits, guinea-pigs, and white mice are extremely susceptible, 
especially so when the bacteria are injected under the skin of 
the animal. A single bacterium injected under the skin of a 
white mouse is sufficient to cause the death of the animal. 
Carnivorous, or flesh-eating animals are, as a rule, more re- 
sistant to the disease than are herbivorous, or plant-eating 
animals. The former are not entirely free from attacks, how- 
ever, as epidemics have at different times broken out in 
zoological gardens among leopards, lions, bears, and other 
animals of this class. Wild deer, elk, and goats are subject 
to occasional outbreaks. 

338. Symptoms of the Disease. — In cattle, sheep and other 
animals which the disease attacks readily, the bacteria 





A B 

Fig. 200. — A. Bacillus anthrax. B. The same with spores. 

multiply rapidly, become enormous in numbers, and swarm 
throughout the entire body of the animal. They float in the 
blood and accumulate in large numbers in the spleen, liver, 
kidneys, and lungs. Internal hemorrhages, or bleeding, occur 
in different parts of the body, a high fever results, and death 
occurs very suddenly. 

In animals which offer a high resistance to the disease local 
infections in the form of large carbuncles develop. If these 
are lanced and kept cleaned out, healing and recovery usually 
occur. Men who handle hides from infected animals often 
have these carbuncles on their hands or shoulders where they 
carry the hides. In such cases, the spores of the organism 
are supposed to enter the body of the victim through the skin. 



PARASITES 301 

Men who handle wool from infected sheep often contract the 
disease in a form which is known as wool-sorter's disease. 
In this case, the spores are taken into the lungs and cause a 
disease resembling pneumonia. 

339. Character of the Bacterium (Bacillus anthracis). — 
The organism which causes this disease is a rod-shaped bac- 
terium and one of the largest of the known pathogenic, or 
disease-causing, bacteria (Fig. 200A). Under certain condi- 
tions, it forms spores which have remarkable powers of endur- 
ance (Fig. 200B) . Spores have been known to remain alive in 
pastures and still be able to cause the disease for as long 
as 30 years. The bacteria can be grown artificially on gelatin 
cultures and, if grown at a suitable temperature (their 
optimum temperature 37°C, or 98%°F., the temperature of 
human blood), they retain their virulence, or disease-causing 
power, and will speedily cause the death of a susceptible ani- 
mal if injected into its body. 

340. Methods of Prevention and Cure. — Since the dis- 
covery of a method of preventing this disease was an event of 
unusual importance in the history of medicine, you will be 
interested in knowing something of the circumstances which 
led to its discovery. The great "Father of Bacteriology," 
Louis Pasteur, discovered the principle involved in the 
method in the year 1880 and perfected the method of pre- 
venting anthrax during the following year. After Robert 
Koch had established beyond all possible doubt that Bacillus 
anthracis is the specific, cause of the disease anthrax, Pasteur 
turned all his powerful energies and his genius to the study 
of infectious diseases. 

At this time, anthrax was known and dreaded all over 
the world and in some years it had caused a loss in France 
alone of 20,000,000 francs, or 4,000,000 dollars. The burden 
of the scourge fell heavily upon the peasants or farmers, 
many of whom had suffered the loss of their entire flocks. 
Pasteur, some years before, had been of great service to the 
peasants of his country by showing them how to avoid the 



302 MICROORGANISMS 

terrible silk-worm diseases which had nearly ruined the silk 
industry of the country. He now longed to find some method 
of combating anthrax. 

He had in his laboratory many cultures of different kinds of 
pathogenic bacteria and among these were cultures of the bac- 
teria that caused the common disease, chicken cholera. He 
had labored so hard and so long with his experiments that he 
was finally forced on account of ill health to take a short 
vacation. This he dreaded to do for he feared that lack of 
care would cause all his valuable cultures to die. 

When he returned to his laboratory, you can imagine his 
dismay when he found that all his cultures were apparently 
ruined. This would have meant that much of his labor had 
been lost and that the final result which he hoped for would 
have been delayed. He made every effort to revive his 
cultures by transferring them to new culture media and among 
other things, he inoculated some chickens with one of these 
old cultures of the bacteria that cause chicken cholera. 
These chickens failed to develop any symptoms of the disease. 
Pasteur considered the cultures lost. 

He was greatly surprised, however, to find that later when 
he inoculated these same chickens from fresh virulent cul- 
tures, they failed to take the disease. He quickly prepared 
other cultures and allowed them to stand in test tubes as these 
original ones had done and then repeated the experiment of 
first inoculating chickens with the weakened cultures and 
then later inoculating the same chickens from fresh virulent 
cultures. He was thus soon able to prepare weakened, or 
attenuated, cultures, as he called them, which would regu- 
larly serve to prevent the chickens from taking the disease 
when inoculated from strong virulent cultures. 

This method of treating, or vaccinating, chickens, as the 
process has come to be called, has never come into general 
use, for later experience showed that some fowls are really 
given the cholera by it. It served, however, to give Pasteur 
a principle to work on. He was soon able to produce a 



PARASITES 303 

vaccine for anthrax which has proved to be of great value. 
Pasteur grew the anthrax bacillus under almost all possible 
conditions and then used them to inoculate well animals. He 
finally discovered that, when the bacteria are grown at a tem- 
perature of from 42° to 43° C., or 107%° to 109%° F., they 
gradually lose their virulence, or disease-producing power, 
but do not lose the power to stimulate the animal to build up 
its resistance to the disease. 

341. Preparation and Application of Anthrax Vaccine. — 
In the ordinary practice of preparing the vaccine, bacteria 
whose virulence has been tested by inoculation experiments on 
rabbits or guinea-pigs, are grown at the temperature of from 
42° to 43° C. for varying lengths of time. "Whenever it is 
found that the culture has been so weakened that it will just 
kill white mice but not quite kill guinea-pigs, about Vi c.e. 
of the culture is injected, into cattle and half this amount 
into sheep. About twelve days later, a similar dose of a cul- 
ture that will just kill guinea-pigs but not quite kill rabbits 
is injected. After this, virulent cultures may be injected with 
impunity, and the animal so treated will not contract the 
disease in any natural way. 

342. Nature of Immunity. — When an organism is free from 
liability of attack by a given disease, it is said to be immune 
or to possess immunity from the disease. All organisms are 
naturally immune to certain diseases that affect other organ- 
isms. Thus man is not at all susceptible to chicken cholera 
or to a good many other diseases that affect domestic animals 
and, on the other hand, the domestic animals are not affected 
by very many of the diseases that affect man. We call this 
sort of immunity, natural immunity. 

But you are familiar with the fact that when you have once 
had an attack of measles or whooping cough you are not 
likely to have these diseases again, even though you be re- 
peatedly exposed to them. You are thus rendered immune to 
these and other diseases by having had them. This kind of 
immunity, we call acquired immunity. 



304 MICROORGANISMS 

You will note that the method of vaccinating an animal 
with an attenuated culture of the organism that causes a 
certain disease gives the animal an acquired immunity against 
the disease without the necessity of the animal's having the 
disease. 

343. Results of Anthrax Vaccination. — Professor Cham- 
berlain was made responsible for the production and distri- 
bution of anthrax vaccine. After twelve years, in 1894, he 
reported that 3,296,815 sheep and 438,824 cattle had been 
vaccinated in France. Only 1 per cent, of the sheep and .34 
per cent, of the cattle had died. At that time it was esti- 
mated that the average annual loss from anthrax among un- 
vaccinated sheep was 10 per cent, and among unvaccinated 
cattle was 5 per cent. 

This single discovery by Pasteur has been, and will be for 
all time to come, of enormous value to stock raisers, through- 
out the world. Vaccination of sheep and cattle and some- 
times of other animals is now regularly practised in all 
countries where the disease occurs. 

2. Vaccination and Smallpox 

You are familiar, in a way, with vaccination against small- 
pox. Since the principle involved in this is essentially the 
same as that in vaccination against anthrax or any other dis- 
ease, a little discussion of smallpox vaccination will serve to 
make the process clearer to you. 

344. The Origin of Smallpox Vaccination. — Prior to about 
the year 1800, smallpox was an extremely common disease. 
It was so very common that few people escaped having it 
sometime during life, and it has been estimated that fifty 
million people died of it in Europe during the eighteenth 
century. In the early part of the eighteenth century, it was 
discovered that, if a little of the pus taken from a patient suf- 
fering with the disease is injected under the skin of a healthy 
person, a mild form of the disease generally results. This 
has the same immunizing result as a more virulent attack of 



PARASITES 305 

the disease which might be contracted in some natural way. 
This practice was introduced into England in the year 1717 
and for over a hundred years was widely practised until it 
was prohibited by an act of Parliament in 1840. The danger 
of this practice lies mainly in the fact that persons artificially 
infected in this way become new centers for the spreading of 
the disease in the virulent form. 

In 1796, Edward Jenner, a country physician, in England, 
observed that persons who had been affected with cow-pox, 
a mild eruptious disease of cattle, were very unlikely to con- 
tract smallpox even when repeatedly exposed to it. This 
led him to recommend, and to practise on his patrons the use 
of the virus of cow-pox, instead of that of smallpox as a 
means of producing immunity to the latter disease. His 
method proved to be a remarkable success and soon came into 
general use. 

At present, the vaccine is produced by inoculating a healthy 
calf with the cow-pox virus and then after about five days, 
the virus of the pustules, which develop near the place of 
inoculation, is removed, mixed with glycerine and kept until 
it is proved to be free from bacteria and other organisms, 
and then it is ready for use in vaccination. 

345. Cause of Smallpox Not Known. — You will note that 
this method of vaccinating against smallpox was discovered 
more or less accidentally long before the germ theory of dis- 
ease came to be generally accepted. Consequently, at the time 
of its discovery, no one had any idea of the nature of the 
process by which the immunity is brought about. We have 
not even yet been able to discover the organism which is 
the cause of this disease, and our only reason for believing 
that it is caused by some microorganism, is its general re- 
semblance to other diseases that are known to be thus caused. 
Since we do not know the organisms, we can judge of the 
nature of the immunizing process only by comparison with 
other better known diseases. From this point of view, it is 
the opinion of most students of the subject, that the organism 



306 MICROORGANISMS 

which causes cow-pox is the same as the one which causes 
smallpox. They believe that in passing through the body of 
the calf, the organism becomes attenuated, or weakened, so 
that it is unable to produce smallpox when introduced into 
the human body, but is still able to stimulate the body to 
build up its defenses against the virulent form of the or- 
ganism. 

346. The Effectiveness of Smallpox Vaccination. — The in- 
frequency of smallpox in recent years, in most countries, as 
compared with the eighteenth century is ample evidence of 
the effectiveness of vaccination as a preventative of the disease. 
More striking evidence, however, can be found in countries 
which require all persons to be vaccinated. 

In 1870-71, during the Franco-Prussian war, the armies of 
both Germany and France were attacked by smallpox. Vac- 
cination had been compulsory in the German army since 1834 
but was not compulsory in the French army. As a conse- 
quence, the French lost 23,000 soldiers from smallpox and the 
Germans lost only 273 from that cause. Vaccination has been 
compulsory in Sweden since 1810. From 1774 to 1801, 
smallpox had caused an annual death rate of 2,050 per 
million of inhabitants in that country. During the years from 
1810, when vaccination was made compulsory, to 1855, the 
death rate had fallen to 169 per million, and in the period 
from 1884 to 1894, the average annual death rate was only 
2 per million. 

This shows that, if all countries would follow the example 
of Germany and Sweden in requiring that every citizen be 
vaccinated, smallpox might entirely disappear from the earth. 
It shows further that as long as frequent outbreaks of the 
disease are allowed to occur as they do every winter in this 
country an individual is very foolish if he does not submit to 
vaccination as often as it will take. 

For about 10 years there has been a rather active campaign 
against vaccination by people who style themselves adherents 
of personal liberty in all health matters. According to statis- 



PARASITES 



307 



tics given by one of the largest life insurance companies, this 
campaign against vaccination has produced increased laxity in 
the practise of vaccinating and there has been a corresponding 
increase in the prevalence of the disease. The statistics given 
are these, from 20 states: 

CASES OF SMALLPOX. 



State 


1916 


1917 


1918 


1919 


1920 


California 

Colorado 


234 

103 

* 

1,158 

2,085 

819 

69 

32 

1,365 

1,270 

1,401 

* 

9 

* 

1,921 

119 

97 
* 

637 

* 


329 

323 

4,996 

4,593 

2,623 

835 

98 

65 

2,929 

2,718 

1,530 
* 

6 
* 

5,243 
122 

380 

1,350 

390 

413 


1,069 

1,680 

3,842 

5,582 

7,130 

950 

219 

27 

4,417 

2,252 

3,601 

3,906 

65 

899 

. 10,227 

493 

612 

4,338 

1,676 

1,266 


1,992 
1,714 
3,971 
3,620 
2,130 
1,120 
212 

32 
2,885 
2,280 
2,511 
2,861 

66 
1,880 
3,924 
2,381 

198 

* 

4,372 
2,214 


4,503 

2,878 
6,617 


Indiana 


6,775 




3,900 




1,558 


Maryland 

Massachusetts 

Michigan 

Minnesota 

Mississippi 

Nebraska 

New Jersey 

North Carolina 

Ohio 

Oregon 


176 
29 
4,848 
5,447 
4,148 
4,135 

181 
2,961 
7,228 
2,828i 


Pennsylvania 

Texas 


215 
1,547 


Washington 


5,997 




2,619 


Totals 


11,319 


28,943 


54,451 


40,363 


68,590 



* No data available. i Up to November 30, 1920, only. 

347. How Often Should One be Vaccinated? — In a report 
of the Board of Health of the city of Berlin, the following 
sentence may be found: "Vaccination in infancy, renewed 
at the end of childhood, renders the individual practically as 
safe from death from smallpox as if that disease had been 
survived in childhood, and almost as safe from attack." In 
a recent report of the Illinois State Board of Health, occurs 
the following sentence: "A recent successful vaccination is a 
positive protection against an attack." Evidently, then, 
everyone should be vaccinated in infancy and at least once 



308 MICROORGANISMS 

after reaching maturity. Anyone who travels or mingles 
much with people in the winter time should be vaccinated 
every four or five years. 

3. Diphtheria 

There is probably no other serious bacterial disease which 
attacks the human race whose story is so well known as is 
that of diphtheria. Our knowledge of the details of this 
disease and of its cure and prevention is well-nigh perfect. 
In constitutes the most complete triumph of the science of 
bacteriology. This being the case, a somewhat detailed ac- 
count of the disease will serve to acquaint us with the general 
theory of bacterial diseases, their cure and prevention. 

348. Discovery of the Organism and Its Relation to the 
Disease (Bacillus diphtheriae) . — In 1883, Klebs discovered 
the organism. In the following year Loffler succeeded in 
obtaining pure cultures of it from the throats of patients suf- 
fering from the disease. This seemed to indicate plainly that 
the organism is the direct cause of the disease. Loffler him- 
self was at that time inclined to doubt this, for he had found 
the same organism in the throats of perfectly healthy children 
and at the same time had failed to find it in the throats of 
some patients who showed strong symptoms of the disease. 
These causes for doubt have since been completely cleared 
away. It is now known that certain other bacteria can 
cause a condition of the throat which is practically indis- 
tinguishable from that caused by the diphtheria bacillus. 
Again, it is now known that some people carry diphtheria 
bacilli about in their mouths and throats and yet are entirely 
unaffected by them. This latter fact is an important factor 
in the spread of the disease, for people who thus carry the 
organisms about may give the disease to more susceptible 
persons. 

The final discovery which proved beyond all doubt the 
relation of the organism which Klebs had discovered to the 
disease was made in 1888-89 by Roux and Yersin. These 
men showed that the organism forms a toxin, or poison, 



PARASITES 309 

which may be separated from the organism and which when 
injected into a susceptible animal, causes all the characteris- 
tic symptoms of the disease. 

349. Symptoms of the Disease. — The organism usually 
finds lodgment and develops on the mucous membrane of 
the throat, nose, and rarely of the lungs. Even the eyes or 
the middle ear may become the seat of infection, though, 
in the great majority of cases, it is the pharynx that it 
affected. The form of the disease that is sometimes called 
membraneous croup is an affection of the larynx. In rare 
cases, the organisms enter the general circulation and spread 
throughout the system. Usually they are confined to some 
local area of the mucous membrane where they develop and 

Fig. 201.— Bacilli diphtheria. 

secrete their toxin, causing a white membrane to develop. 
The toxin is absorbed into the system where it attacks cer- 
tain vital organs, principally the heart, nerves, and kidneys. 
In these organs, it causes a fatty degeneration and, therefore, 
a weakening of the organs. 

350. Character of the Organism. — The diphtheria bacillus 
is a slender rod-shaped organism of moderate and somewhat 
variable size (Fig. 201). When it is stained, it presents a 
sort of beaded or granular appearance which is so character- 
istic that a trained bacteriologist can recognize it with cer- 
tainty. This makes possible certain diagnosis of the disease 
and enables the physician to determine with certainty when a 
patient may safely be freed from quarantine. 

The organism grows readily on several kinds of common 



310 MICROORGANISMS 

food, especially milk, if kept at a suitable temperature. This 
fact is important in the spread of the disease, for many 
epidemics have been known to have been caused by the 
handling and distribution of milk by persons suffering with 
a mild attack of the disease. 

The organism is not known to form spores but it has a 
high resistance to drying. It has been known to live and 
retain its virulence for several months in dried membrane or 
sputum. This makes necessary the disinfection of houses in 
which cases have occurred. 

351. Nature of the Toxin. — "When the bacteria are grown 
in a broth, a soluble toxin is produced in the broth. The 
broth is now passed through a fine porcelain filter. The filter 
retains the bacteria but allows the broth and soluble toxin 
to pass through. 

This soluble toxin, without the bacteria, when injected 
into the body of a healthy animal, produces all of the symp- 
toms of the disease except the formation of the false mem- 
brane in the throat. The membrane is formed, in normal 
cases, by the bacteria themselves. The absence of the* bacteria 
accounts for the failure of the membrane to form although all 
other symptoms are present. 

Little or nothing is known of the chemical nature of the 
toxin, or of the manner in which it is produced. It is only 
known that it is a powerful poison thrown out from the bodies 
of the bacteria and that it attacks certain tissues of the animal 
body. 

352. The Antitoxin. — In 18*90, Behring and Kitasato took 
the next step in the mastery of this disease. They dis- 
covered a method of producing an antitoxin which is both a 
cure and a preventive of the disease. They experimented 
with rabbits, first inoculating them with attenuated (weak- 
ened) cultures of the bacteria and later with more virulent 
cultures. This treatment made the rabbits entirely immune 
from the disease. Next, these experimenters discovered that 
the blood serum of these rabbits which had been made im- 



PARASITES 311 

mune from the disease, when injected into the bodies of other 
rabbits which had been inoculated with virulent cultures of 
the diphtheria bacilli, had the power of neutralizing, or 
destroying, the toxin produced by the bacilli. 

In other words, they discovered that the blood serum of 
the rabbits which had been made immune from the disease by 
being inoculated with the bacteria contained some substance 
which destroyed the toxin produced by the diphtheria bacilli. 
It is believed that the diphtheria toxin always stimulates the 
body of an animal to produce this neutralizing substance, the 
antitoxin, as it is called. 

The next problem was to cause the body of an animal which 
stood a chance of being exposed to the disease to produce this 
antitoxin in sufficient quantities to prevent his contracting 
the disease. That is, to use the antitoxin as a preventive 
of taking the disease. 

It is now known that the body of a well animal can be made 
to produce this antitoxin by inoculating it with toxin al- 
though there is no bacteria in the inoculating serum. An 
animal whose body is producing antitoxin, rarely, if ever, 
contracts the disease when exposed to diphtheria bacilli. The 
virulence of the disease is also greatly lessened by the use of 
the serum if inoculation is made as soon as the patient con- 
tracts the disease. 

353. Preparation of the Antitoxin. — The antitoxin for 
the treatment of diphtheria today is manufactured in the 
bodies of healthy horses. The methods by which this anti- 
toxin is secured are of the most painstaking and careful 
kind. Every possible precaution is taken to insure the purity 
and safety of the antitoxin. The story is too long and tech- 
nical to be told here. The use of the diphtheria antitoxin is, 
however, universal in the treatment of the disease. 

354. Results of the Use of Diphtheria Antitoxin. — Ever 
since the early nineties of the last century, the horse serum for 
the treatment of diphtheria has been in common use through- 
out the civilized world and its effect on the death rate from 



312 MICROORGANISMS 

this disease has been remarkable. This is shown by the fol 
lowing table which shows the average death rates, from 
diphtheria, per 10,000 of population in the leading cities of 
the world during the decade just preceding and the one just 
following the introduction of the serum. 

1885-1894 1895-1904 

Before use of Antitoxir 

Antitoxin Period 

Paris 6.41 1.49 

Berlin 9.93 2.95 

London 4.85 3.88 

New York 15.19 6.62 

Boston 11.76 6.34 

Chicago 14.29 5.13 

It might appear that, since the serum is such a perfect cure 
for the disease, the death rate should be reduced much lower 
than the preceding table shows. It is a fact, however, that 
for the best results the serum needs to be used in an early 
stage of the disease. Since there are so many other types of 
sore throats which may be confused with an early stage of 
diphtheria, many people fail to call a physician in time to 
give the serum a fair chance. 

355. Antitoxin As a Preventive of Diphtheria. — Diph- 
theria antitoxin is not only a specific cure for the disease but 
it has been found very effective also as a preventive. When 
a case of diphtheria breaks out in a family, the physician who 
attends the case, the nurse, /and members of the family who 
are liable to exposure are generally given regular doses of 
the serum. This treatment is usually effective in preventing 
further spread of the disease. 

4. Other Bacterial Diseases 

It will be impossible for us to consider other bacterial dis- 
eases as fully as we have considered diphtheria. This study, 
however, has given us considerable knowledge of the general 
theory of such diseases and some brief mention of some of the 
more important ones that remain will be of value, 



PARASITES 313 

356. No Two Diseases Just Alike. — It might appear to you 
that, since we have worked out so perfectly methods of cure 
and prevention for one bacterial disease, it should be easy to 
work out similar methods for all other diseases. This is far 
from being true. To understand this, you must remember 
that these different diseases are caused by different species 
of bacteria and that these different species vary widely in their 
characteristics and in their relations to the animal body. For 
example, not all disease-causing bacteria produce a soluble 
toxin which can be easily separated from the organism and 
used in the production of antitoxin as in the case of diph- 
theria. Again, the antitoxins, when produced, are not always 
so effective in the neutralization of the toxin or so harmless 
to the body of the patient as is that of diphtheria. Many 
other differences exist which can not be explained here because 
of the technicalities and difficulties they involve. It is enough 
to say here that almost every bacterial disease presents its 
own peculiar difficulties and that little headway has been 
made up to the present time in dealing with some of them. 

357. Prevention and Cure. — In general, it may be said that 
the efforts of bacteriologists in seeking to gain control over 
bacterial diseases are directed along three general lines. 

First, they seek to find some method of preventing the dis- 
ease, by giving the people or animals artificial immunity 
from the disease. As a result of efforts along this line we 
have the various vaccines, such as Pasteur's vaccine against 
anthrax which consists of attenuated cultures of the bacteria, 
and the cow-pox virus as a vaccine against smallpox. When 
vaccines are used, you will note that the body of the patient 
is stimulated by the presence of the toxin or the attenuated 
bacteria to secrete its own antitoxin or to raise its resistance 
to the disease in some other way. 

Second, the bacteriologists seek to find some method of pro- 
ducing an antitoxin and therefore a cure for the disease as 
in the case of diphtheria. 

Third, bacteriologists seek to learn the methods by which 



314 MICROORGANISMS 

the different diseases are ordinarily spread from patient to 
patient. Knowing this, they are able to devise methods of 
preventing such spread of the disease. 

It is evident that the first two of these lines of effort must 
be left to the bacteriologists and physicians but it is quite as 
evident that the value of the known methods of preventing 
the spread of disease depends very largely on the faithful co- 
operation of all the people. Therefore, it is quite important 
that as nearly as possible, every one should come to know how 
the common diseases are ordinarily spread and how this 
spreading might be prevented. For this reason, this latter 
phase of disease should be emphasized. 

5. Important Facts about Common Diseases 
358. Pneumonia. — This is primarily a disease of the lungs 
and is usually caused by a certain spherical bacterium called 
pneumococcus. In most serious cases, however, the organism 
finds its way into the general circulation and is distributed 
over the body. While pneumococcus is the cause of a 
majority of the cases of pneumonia, other organisms, such as 
Bacillus diphtherias, and Bacillus influenzas, and others may 
cause an inflammation of the lungs which is difficult to dis- 
tinguish from that resulting from pneumococcus. Often two 
or more of these organisms are involved in an attack of the 
disease. 

Pneumococci and the several other organisms which may 
cause this disease are very widespread and are very com- 
monly present in the mouths and throats of healthy persons. 
As long as the body is in a vigorous state of health, however, 
it is usually able to ward off an attack but often when weak- 
ened by other illness, or by exposure to extreme cold, hunger, 
fatigue, or lack of fresh air or other similar causes, the re- 
sistance of the body seems to break down and the disease 
gets a start. This fact explains why the disease so often 
follows .other forms of illness and also why it is more preva- 
lent in the winter time than in the summer. Lack of fresh 



PARASITES 315 

air in the winter time is a fruitful cause of pneumonia. Hence 
it is evident that the surest means of escaping this disease 
lies, not in an effort to escape the bacteria for that is prac- 
tically impossible, but in keeping the body in a vigorous state 
of health. Fear of this disease should be a strong stimulus 
to sanitary living. Good food in moderate amounts, warm 
clothing, plenty of exercise, and plenty of fresh air are the 
best means of protection against this disease. 

A person who has suffered one attack of pneumonia shows 
little or no increased resistance to a second attack. There- 
fore, it seems that the organism does not form a soluble 
toxin nor does it stimulate the body to form an antitoxin. 
Consequently, we have no serum treatment for it of any 
kind. It is not definitely known just how the body finally 
overcomes the organism and recovers. 

359. Typhoid Fever. — This is one of the most common 

and important of all bacterial diseases 

(Fi<£ 202) and yet it need not be if every 

one knew and practised some very simple Z^S^f 

things concerning it. The disease affects . Tv 

primarily the alimentary tract and is con- T*" 

tracted almost wholly by taking the organ- „ .£ IG - 202 - 

• + +i. ^ -j-x. £ j j • 1 Bacillus typhosus. 

ism into the mouth with food or drink. 

The organism escapes from the body of the patient suffering 
from the disease with the wastes from the alimentary tract 
and in the urine. 

Since the organism can not multiply or live for any great 
length of time outside the human body, it is evident that it 
must be carried more, or less directly from the wastes of the 
sick patient to the alimentary tract of the next victim. This 
transfer could be cut off if all the wastes from sick patients 
and convalescents everywhere were treated with disinfectants 
as soon as removed from the body. If this is not done, how- 
ever, there are many ways in which the organisms may be 
spread to other persons. Flies may carry them directly to 
the food or water used by healthy persons; the nurse and 



ftS* 



316 MICROORGANISMS 

other persons who wait upon the patient may carry them on 
their hands to the food or dishes used by other members of 
the family ; they may get into water supplies or wells, into the 
milk distributed by dairies, or on fresh fruits and vegetables 
distributed by groceries and be widely spread through a 
community. In many such ways the transfer of the organisms 
from the wastes of the sick patient to the food or drink of 
healthy persons is accomplished if they are not destroyed at 
once by the use of disinfectants. 

If the wastes from a typhoid patient are all collected in a 
suitable vessel and treated with a 5 per cent, solution of car- 
bolic acid for an hour before they are put into the sewer or 
outdoor vault, and if due care is taken by those who attend 
the patient, there is little chance for further spread of the 
disease. This sterilization of the wastes needs to be kept up, 
however, until the patient is known to be free from the organ- 
ism. The time when a patient is free from the organism 
after recovery can be determined by a bacterial examination. 
Some persons recover from the disease and yet carry myriads 
of the organism for months or even years and may, all the 
time, be a source of spread of the disease. Such persons are 
known as typhoid carriers. 

We do not have any successful serum treatment for typhoid 
fever but we do have vaccines which consist of the dead 
bacteria or materials derived from them that have proved 
wonderfully successful in rendering persons immune from the 
disease. Soldiers in the armies are regularly vaccinated 
against typhoid now and the result is that this disease which 
was once a principal danger to the soldier has, in many in- 
stances, nearly disappeared from the army camps. Vaccina- 
tion is also widely practised in cases of epidemic outbreaks of 
the disease among private citizens. The immunity produced 
either by an attack of the disease or by vaccination is only 
temporary and so vaccination must be repeated at intervals. 

360. Influenza or Grippe. — This very common disease is 
now known to be caused by a very small rod shaped bacterium 



PAEASITES 317 

known as Bacillus influenzae. This disease is of common 
occurrence, especially in the winter time, and at times has 
swept over the country as severe epidemics. The organism 
generally invades only the mouth, throat, and air passages, 
the toxin being absorbed from such local infection. It fol- 
lows from this that the organism is expelled from the body 
of the patient mainly through coughing and sneezing and in 
the sputum. It has been found that very little drying serves 
to kill the organism and therefore the disease is generally con- 
tracted through rather intimate association with a patient or 
convalescent. Due observance of this fact may enable one 
to avoid contracting the disease. 

361. Common Colds. — What we commonly call "bad colds' ' 
are infectious diseases which are due to a variety of organ- 
isms. Streptococcus, pneumococcus, and the bacilli of influ- 
enza and diphtheria as well as other organisms may each be 
the cause of what is generally regarded as a bad cold. The 
first stages of the more virulent diseases caused by these 
organisms show essentially the same symptoms as a cold. 
This fact makes a cold deserving of more serious attention 
than it commonly receives. When one goes about his work, 
mingling with other people, while suffering from a cold, he 
is not only running a serious risk himself, but is exposing 
other people to danger. We should be taking a long stride 
toward the prevention of several serious diseases, if we could 
induce everyone to give proper attention to bad colds. 

362. Tuberculosis. — This disease is often spoken of as the 
great white plague, and it richly deserves that name for it 
is, each year, responsible for more deaths than any other 
single cause. It has been estimated that in 1907, 153,000 per- 
sons died from tuberculosis in the United States. It has also 
been estimated that it costs the people of the country annually 
$200,000,000. Another bad feature of the disease is the fact 
that it usually results in a comparatively early death. The 
average age of persons dying from tuberculosis in the U. S. 
has remained at about 35 years ever since 1860, when 



318 



MICROORGANISMS 



statistics first began to be collected. Death at this age is 
about the saddest, for it usually means broken families and 
motherless and fatherless children. Another bad feature of 
the, disease is that it usually means a long lingering illness 
that is more or less hopeless. 

It is difficult to paint the picture of this disease too darkly. 
It is important that everyone come to know how great a 
scourge it is. If every citizen could realize how great a dan- 
ger threatens him from this source we might have a more 
united effort in our endeavor to do away with the disease or 
lessen its attack. 

There is hardly any part of the human body that the 
tubercular bacillus (Fig. 203) may not attack. The lungs 
constitute the chief seat of infection but the intestines, the 



-- ' ".- ~Z$?4~'u >- 


*gmm^ 


' M 1& 


A ^:^f A^fe^k, 




^Sl^P^&L' 


. ',', 


r^V^My 


\i' '-*:* "V '' 


% ' } V < . 




' ' ."" * **"*' .-- «..'.--; ." 



Fig. 203. — Tuberculosis bacilli. 

various glands of the body, the skin, the throat, the bones and 
joints and other parts of the body are frequently attacked. 
The organism generally finds entrance to the body through 
the mouth or nose and it also leaves the body to become a 
source of infection to others through the same openings. 
The sputum of a consumptive contains myriads of organisms. 
It has been found that in dried sputum, some of these organ- 
isms may retain their vitality for as long as eight months. 
These facts make it evident that all sputum from tubercular 
patients should be completely destroyed or sterilized. The 
droplets of water that are usually thrown violently into the 
air when a tubercular patient coughs or sneezes usually con- 



PARASITES 319 

tain great numbers of the bacteria and are thus a source of 
danger to others intimately associated with the patient. 
Spoons, forks, and dishes used by a tubercular person are 
likely to be infected with the organism and should always 
be sterilized by boiling water before they are used by others. 
Strict observance of these and other similar precautions may 
enable one to live in the same family with a tubercular per- 
son and yet avoid infection. 

363. Where Danger Lurks. — It seems that the average 
healthy person has a rather high natural resistance against 
tuberculosis, provided that he is properly conditioned. Many 
occupations and customs of modern life are highly conducive 
to the contraction of the disease. People who work indoors, 
particularly where there is much dust, poor ventilation, and 
bad sanitary conditions, are much more likely to contract 
the disease than are those who work in a better environment. 
This is shown by the following table which shows the number 
of persons per 100,000 of population in the specified occupa- 
tions, who died from tuberculosis of the lungs in the year 1900. 

Occupation Number of deaths per 100,000 

Marble and stone cutters 540.5 

Cigar makers and tobacco workers 476.9 

Compositors, printers, and pressmen 435.9 

Servants 430.3 

Bookkeepers, clerks, and copyists 398.0 

Laborers (not agricultural) 370.7 

Farmers 111.7 

Other sickness such as measles, whooping cough, scarlet 
fever, and influenza which leave the body in a weakened con- 
dition are often a predisposing cause of tubercular infection. 
During attacks of these and similar diseases and during con- 
valescence, one should be extremely careful to avoid all 
chance of tubercular infection. 

We often hear the statement made that tuberculosis is 
hereditary and that it tends to run in families. While the 
former statement is entirely untrue, it is doubtless true that 



320 • MICROORGANISMS 

susceptibility to the disease does run in families, or in other 
words, that the amount of resistance against the disease is a 
matter of heredity. For this reason, people who have tuber- 
culosis in the family need to be extremely careful to avoid 
infection and to avoid conditions which are conducive to in- 
fection, for they are likely more susceptible than are others 
who have no tuberculosis in their ancestry. 

364. Tuberculosis Curable. — We hear a good deal in these 
days in newspapers, in popular magazines, and in the adver- 
tisements of sanitariums to the effect that tuberculosis is a 
curable disease. This is no doubt true and the means of cure 
sound comparatively simple. They consist of rest, plenty of 
fresh pure air day and night, and plenty of good wholesome 
food. But no one should be deluded by the fact that the 
disease is curable by these means into being careless about 
contracting it. One great danger of the disease lies in the 
fact that one may be affected by it for months or even years 
before the fact is easily determined and then it is often too 
late to. hope for a cure. If one is once seriously infected 
with tuberculosis, he is not likely ever to be able to do 
much else but obtain a cure; if he is ever successful in so 
doing. 

Many people with apparently high resistance have slight 
attacks of tuberculosis and recover without ever knowing that 
they had it. One investigator made a comprehensive study 
of the bodies of 500 persons who had died from various causes, 
and he found evidences of former tubercular infection in 97 
per cent, of the bodies. Doubtless most of these people had 
never known of the attack. 

Our chief defenses against this disease are our natural 
resistance, and vigorous health. As long as the disease is as 
prevalent as it is, we can hardly hope to escape entirely 
chances of infection. We should do what we can to escape 
the organism but we should rely mainly on being able to 
overcome it when it attacks us. We should all try to live all 
the time much as a tubercular patient must live. We may not 



PUBLIC HEALTH 321 

need so much rest but we all need the fresh air and the whole- 
some nourishing food. 

III. PUBLIC HEALTH 

365. Our Duty Regarding Public Health. — It is perfectly 
evident that in matters that have to do with health, no one 
lives unto himself alone. One may do much for his personal 
health through proper attention to personal cleanliness, to 
food and clothing, to fresh air and exercise but in the matter 
of contagious diseases, no one person by his own efforts can 
guarantee his own safety. Those who supply us with milk 
and other foods may bring infection to us, we may get it from 
those with whom we associate, or we may get it from the 
strangers with whom we mingle as we travel. The city water 
supply may give us disease, or flies may carry it to us from 
garbage or sewage which are not properly disposed of. We 
may be endangered by the failure of public officials to prop- 
erly enforce quarantine. In all these ways, we are dependent 
on others for protection against disease. If these others on 
whom we depend for protection are ignorant or careless, we 
are bound to suffer. 

If we would seek to better our conditions with reference 
to contagious diseases, we must rely mainly on our efforts to 
raise the general level of intelligence and sense of responsi- 
bility in regard to these things on the part of the whole 
people. Every one who has the grand privilege of a high 
school education and who learns concerning matters of health, 
even what may be learned in this book, should consider 
himself or herself eligible for leadership in matters of public 
health. There are needed in every community many people 
who will practise good sanitation and observe all the laws 
of public health and who will insist that others do the same. 
"What we learn in school should be for use in our daily lives 
and it is to be hoped that what you have learned here con- 
cerning health and disease will be made a foundation for 
your daily practices. 



CHAPTER VII 

Food — Its Uses and Preparation 

I. THE DIET 

366. The Essentials of Human Life. — Air, water, food, 
clothing, and shelter are necessary to maintain human life. 
Without air, death soon results. Without water death from 
thirst follows. Without the proper kind and amount of food 
starvation begins, the body becomes weak and less able to 
resist disease and death results. Acute starvation from utter 
lack of food is not commonly met, but slow starvation is all 
too common. Clothing and shelter are needed to protect the 
person from the inclement weather of the Temperate Zone. 

367. Relative Costs of the Essentials. — Air is the cheapest 
of the essentials, yet it is not free as is sometimes supposed, 
as the providing of fresh air in cold climates costs money. The 
cost of water is not considerable, perhaps $5.00 a year would 
supply a family of six with the water needed for sanitary and 
drinking purposes. Food, clothing, and shelter are all costly 
essentials. Which costs the most depends largely upon the 
habits of the family or individual, but usually the cost of food 
exceeds the cost of either of the others. 

368. Importance of Studying the Food Problem. — The 
business of obtaining food is the most important one in which 
man is engaged. This business includes, not only agriculture, 
which is the art of obtaining foods indirectly from the soil, 
but also the carrying of the food from the farm to the market, 
the milling, the packing, and the other manufacturing 
processes by means of which the food is prepared for the 
consumer, and the retailing of the finished product to 
the consumer. A large portion of our population is engaged 
in the work of obtaining, transporting, preparing, and retail- 

322 



THE DIET 323 

ing food. The food bill of our country amounts to more than 
any other single bill. 

With the early pioneer, the food problem was comparatively 
simple. He raised his own wheat and corn. He took them to 
mill and had them ground into flour or meal. His wife made 
the bread in her own kitchen. The pioneer produced his own 
meat and slaughtered it himself. He produced his own sugar, 
maple sugar, or sorghum. He produced, of course, his own 
milk, butter, and cheese. Very few foods were purchased at 
the grocery. 

Now all is changed. Even the farmer often buys his flour, 
meat, cheese and butter. The population of cities has largely 
increased. Food must be produced for city dwellers as well 
as for those directly engaged in the production of food. "We 
have a greater variety of foods offered for sale in our modern 
markets than the pioneer ever thought of. Food is brought 
from all parts of the world. Much of the food offered for 
sale has passed through one or more manufacturing processes. 
The problem of getting food in these days is, not only a ques- 
tion of getting enough to eat, but it is also a problem of select- 
ing the best and the cheapest foods from the great varieties 
offered for sale in the markets. 

369. What Foods Do for the Body. — We eat that the body 
may be kept in health. Health demands that the foods shall 
keep the body strong and vigorous. The foods must supply 
the body with the materials of which it is made. They must 
also supply the body with energy (Art. 81) so that its work 
may be carried on. In some respects, foods are to the body 
what coal or gasoline is to the steam or gasoline engine. The 
fuel must be burned in the engine in order to make the engine 
go. In a similar way, the foods eaten supply the body with 
the energy to do its work. But the foods do more for the body 
than the fuel does for the engine. The foods provide for the 
growth and the repair of the body. The fuel does no such 
thing for the engine. The engine is not self-repairing by 
the fuel supplied to it. If one part wears out it must be 



324 



FOOD— ITS USES AND PREPARATION 



replaced by a new part from the machine shop. It is evident 
then that the foods must furnish the oody with the materials 
out of which it is made as well as furnish it with energy. 
370. What Substances Must the Foods Furnish to the 
Body? — While the body is known to be composed of many 
complex chemical compounds, it is also known that these 
compounds are composed of but few chemical elements (Fig. 
204). 



Hronoeen »% 

HITfitXBHjJi 
[CALCJUM *7» ** 

, e&QiPttaeivs i^fc 
I omen titr-nwj tl 



Fig. 204. — The composition of the human body. 

Chemical Elements in the Human Body 





Per cent. 




Per cent. 


Oxygen, 


about 65.00 


Sodium, 


about 0.15 


Carbon, 


about 18.00 


Chlorine, 


about 0.15 


Hydrogen, 


about 10.00 


Magnesium 


, about 0.05 


Nitrogen, 


about 3.00 


Iron, 


about 0.004 


Calcium, 


about 2.00 


Iodine 




Phosphorus, 


about 1.00 


Fluorine 


-Very minute trac 


Potassium, 


about 0.35 


Silicon j 




Sulphur, 


about 0.25 







The oxygen, carbon, hydrogen, and nitrogen are the ele- 
ments to which most attention is directed. The carbon and 
nitrogen come exclusively from the foods eaten. Much of the 
oxygen in the body comes from the air we breathe and the 
water we drink. Water also supplies much of the hydrogen 
found in the body. The other elements are usually present in 
the food in such abundance that we give very little thought 
to getting enough of them. 

371. Foods Must Supply the Body with Energy. — The 
gasoline engine transforms the chemical energy (Chap. XI) 
of the gasoline into heat and power. The body likewise 
transforms the chemical energy of foods into heat, muscular 



THE DIET 325 

activity, power to digest foods, power to think, to see, to feel, 
to hear; in short, into all processes included in "life." 

372. How the Energy of Foods is Liberated to the Body. 
— Just as the fuel for the engine must unite with oxygen in 
order that its energy may be delivered to the engine, so the 
materials composing the food must undergo oxidation in the 
body in order to liberate their energy to the body. However, 
in the case of the fuel, the oxidation is rapid and takes place 
at a high temperature. Such oxidation is known as combus- 
tion. In the human body, oxidation is slow and proceeds at 
the body temperature. The process is called slow oxidation. 
Without this slow oxidation there is no liberation of energy 
to the body. Hence, it .is evident that oxygen is just as 
necessary as food for the maintenance of the body activities. 
The oxygen comes from the air. As a result of the combina- 
tion of oxygen with the two most important elements found 
in foods, viz., carbon and hydrogen, carbon dioxid and water 
are the common products. 

Exercise 69. — To Show That Water and Carbon Dioxid Are Pro- 
duced in the Human Body 

(a) Blow the breath against a cold window pane or some other 
cold surface and observe the film of moisture deposited. Where 
did the water come from? In what state was it in the breath? In 
what state is it now on the cold surface? What caused the 
change? Much of the moisture expelled in the breath comes from 
the water drunk, but a part also comes from the water formed in 
the body by the combination of the hydrogen of foods with 
oxygen. 

(b) By means of a glass tube blow the exhaled breath through 
clear lime water contained in a'clean bottle. What happens to the 
limewater? What substance does it show is present in the exhaled 
breath (Ex. 26 f) ? Now take a bottle filled with such air as you are 
inhaling, place some clear limewater in the bottle, cover the mouth of 
the bottle, and shake the liquid with the contained air. What hap- 
pens to the limewater? Can you detect any evidence of carbon 
dioxid in this fresh air? Was carbon dioxid more abundant in the 
exhaled breath than in the inhaled breath? Where did the extra 
amount come from? 



326 



FOOD— ITS USES AND PREPARATION 



373. Where Do the Foods Obtain Their Energy? — It is a 

notable fact that all energy-giving power of the foods of 
animals and of the higher plants is traceable to the work of 
green plants. Green plants are the only living things in all 
the world that have the power to take up the non-nutritious 
materials like water, carbon dioxid, and mineral matter and 
build them into the nutritious foods like sugar, fat and pro- 
tein. If we eat the flesh of an animal, we are still dependent 
upon the green plant for our food, for the animal either got 
its food from plants or from some other animal which sub- 
sisted on plants. Sunlight is necessary for the growth of the 
green plant. Sun energy is taken into the plant through the 
leaves and is stored in the food made by the plant. Thus it 
is that the green plants are. the food factories of the world, 
gaining their raw materials from the earth and the air, and 
storing in the finished product the energy derived from 
the sun. 




Fig. 205. — The carbon cycle. 

374. The Carbon Cycle. — Of the raw materials coming to 
the green plant, water and mineral matter come to it from 
the earth by way of the roots, while the carbon dioxid is 
absorbed through the leaves. Out of the raw materials and 
with the energy derived from the sun, the plant makes a 
simple sugar in the leaves. Oxygen is liberated at the same 
time. This escapes into the air. From the simple sugar, the 
plant, by means of other materials, produces other foods. 
"When the plant or an animal consumes the food the plant 



THE DIET 327 

has produced, oxygen is taken from the air, the food is 
oxidized, its energy is liberated, and carbon dioxid and 
water are produced. The carbon dioxid is returned to the 
air, subsequently to be built into a food again by some green 
plant. This round of changes goes on continually. It is 
known as the "carbon cycle" (Fig. 205). All of the energy 
possessed by fuels is traceable to the work of green plants. 

375. What Is Food?— 

Definition. — A food is anything from which the body may 
obtain its substance and energy. 

Many of the substances we eat furnish both of these for 
the body and are therefore rightly called foods. Some of the 
other substances we eat and which are sometimes called foods, 
are without the ability to supply the body with energy. 
They ought not to be thought of as foods in the same sense 
as those materials which furnish both for the body. Thus 
our meats and cereals supply both for the body. They are 
foods. Salt and water which are taken into the body yield 
no energy to the body. They are not to be thought of as 
foods in the same way as we think of meats and cereals. 

376. Classes of Foods. — Our foods may .be broadly classed 
as foods derived from animals and foods derived from plants. 
The animal foods include such foods as beef, pork, mutton, 
fish, game, poultry, milk and its products, and eggs. The 
foods derived from plants include a greater variety. The 
cereals such as corn, wheat, oats, rye, rice, and barley are 
used. Other plant materials such as the potato, pea, bean, 
sugar cane, sugar beet, and nuts are used. Still other plant 
materials commonly called fruits are widely used. 

377. Man's Quest of Food. — Seeking food has always been 
an important task with man. The earliest races obtained their 
food by gathering edible portions of plants as tender stems, 
roots, seeds, and fruits. These foods were bulky and large 
quantities were required to meet the needs of the body. Had 
it not been for their ability in hunting and fishing, these early 
men would have found it impossible to live on such vegetable 



328 FOOD— ITS USES AND PREPARATION 

foods as they could gather. In those far off times plants were 
not cultivated nor animals domesticated. All food was eaten 
uncooked. (Art. 1 and Art. 65.) 

378. The Discovery of Fire and the Invention of Cooking. 
— "With the discovery of fire simple cooking began. This might 
have consisted of laying the food upon the hot coals or of plac- 
ing it in rude ovens previously heated by making fires in 
them. Cooking food in water was out of the question until 
vessels capable of holding water and withstanding the fire 
could be produced. The discovery of fire made possible the 
manufacture of pottery and the extraction of metals from 
their ores. Thus vessels suitable for use in cooking were 
made. 

379. Cookery and Agriculture. — Dr. Harry Campbell of 
London has shown that the invention of cookery led to agricul- 
ture. He holds that the vegetable foods of early man were 
bulky and required much labor to secure an adequate supply, 
while the seeds of plants, although less bulky and more highly 
nutritious than other parts of the plants, were so hard that it 
was difficult to eat such parts raw. With the coming of cookery 
it became possible so to soften the seeds that they became edi- 
ble. As a consequence man turned his attention to cultivating 
the seed producing plants, because by that means he could 
obtain his vegetable diet with less labor than by simple 
foraging. This marked the beginning of agriculture. Find- 
ing it easier to domesticate certain animals than to capture 
them in the chase, primitive man turned his attention to 
breeding animals that would furnish his meat, milk, and 
skins, the last, of course, serving for clothing. Thus animal 
husbandry arose as a branch of the agricultural industry. 

380. The Food Principles. — While there is a great variety 
of substances used as food, it has been found that they are all 
made up of a few essential substances called the food prin- 
ciples. These include: (1) fats, (2) carbohydrates, and 
(3) proteins. It is from these food principles contained in 
greater or less amount in our common foods that the body 



THE DIET 329 

derives its energy and nearly all of its substance. Mineral 
matter and water are sometimes included in the food princi- 
ples, but they yield no energy to the body. 

381. The Fats. — Fats are composed of carbon, hydrogen, 
and oxygen. They are found in plants and animals in both 
the solid and the liquid states. The liquid fats are frequently 
called oils. But the oils would become solid at a sufficiently 
low temperature. Petroleum and its products, though com- 
monly called oils, are not fats. They are without food value 
to the body. 

Our common fats come from animals, from the cotton seed, 
from corn, from the olive, and from certain nuts such as the 
peanut and the cocoanut. 

382. Carbohydrates. — Like the fats, the carbohydrates are 
compounds of carbon, hydrogen, and oxygen but in different 
proportions from those in fats. Carbohydrates are found 
chiefly in plants, no considerable amount of them coming from 
animal bodies. The following list includes the commoner 
carbolrydrates : 

1. Cellulose (cotton is nearly pure cellulose). 

2. Starch. 

3. Sugars. These include not only common sugar (sucrose) 
which is derived from the sugar cane, sugar beet, and sugar 
maple, but also milk sugar (lactose) found in milk, fruit 
sugar (fructose) found in ripe fruits, glucose (dextrose) the 
chief sugar of glucose syrup, and malt sugar (maltose) de- 
rived from grains. 

4. Dextrin (commonly used as an adhesive). 

Cellulose is not an important constituent of human foods, 
although it plays an important part in animal foods. Starch 
and all of the above sugars are valuable foods, while dextrin 
is unimportant being found in small amounts in glucose syrup. 

383. Simple Tests for Carbohydrates. — 

Exercise 70. — Tests for Carbohydrates 

1. The Sugars Melt. — Place half a teaspoonful of granulated 
sugar in a large spoon and carefully heat it until it melts. 



330 FOOD— ITS USES AND PREPARATION 

2. The Carbohydrates Char When Heated Hot Enough. — 
Continue to heat the melted sugar until a solid black residue, car- 
bon, is left behind. This residue contains most of the carbon that 
was in the original sugar. Repeat the charring test with starch. 

3. The Iodine Test for Starch. — Apply a drop of iodine solu- 
tion by means of a pipette to a little starch (Fig. 206). What 
color is produced? Apply the iodine test to the inside of the fol- 
lowing grains, corn, wheat, oats; also apply it to the following 
fruits and the vegetable, apple, banana, potato. In which ones of 
these do you find starch? If possible compare ripe and green fruits 
as to the presence of starch. 

384. Proteins. — These substances contain nitrogen in addi- 
tion to carbon, hydrogen, and oxygen. Many pro- 
teins also contain sulphur and phosphorus. The pro- 
teins are found in the cereals, in many vegetables, 
in meats, in milk and its products, in cheese and 
butter, and in eggs. The skin, hair, and nails con- 
tain protein substances. Wool and leather, glue and 
gelatin also contain protein substances. The white 
of egg is nearly pure protein mixed with water. 
Milk is a mixture of protein, fat, carbohydrate, min- 
l eral matter, and water, while cheese is a mixture 

of the same substances, but with less water. 

—Using The proteins are the most expensive of the food 
the pip- principles. Animal bodies are generally rich Jn 
proteins and poor in carbohydrates, while the cereals 
are relatively poorer in proteins but rich in carbohydrates. 

Exercise 71. — Tests for Proteins 

1. The Burning Test. — Because of the nitrogen they contain, 
protein substances burn with a characteristic odor, that of burnt 
hair. Burn a little wool and note the odor. Compare it with the 
odor arising from burning cotton. Heat a little wheat flour and 
dried beef in separate evaporating dishes or crucibles. Note the 
odor of the burning materials. 

2. The Ammonia Test. — When protein substances are heated 
with lime (calcium hydroxid, not the solution, but the dry ma- 
terial) ammonia is produced. The ammonia may be identified either 
by its odor or by the fact that it turns moist red litmus paper blue. 
Place small equal amounts of dry gelatin and lime in a test tube 



THE DIET 



331 



AMMONIA GAS 




Fig. 207.— Test for 
proteins. 



and mix them. Heat the mixture strongly, holding a piece of moist 
red litmus paper in the gases escaping from 
the tube (Fig. 207). Be careful that the 
paper does not touch the side of the tube 
where it may meet lime which would turn 
the paper blue just as the ammonia does. 
When you get a strong test for ammonia, 
note the odor of the gases escaping from 
the tube. Disregard the odor of burnt 
hair and give attention only to the ammo- 
nia. Ammonia was formerly made almost 
entirely by heating animal products with 
lime. The ammonia was called spirits of 
hartshorn because the horns of the hart 
deer were frequently used as the animal 
substance. (See Art, 440.) 

3. The Nitric Acid Test. — Place a lit- 
tle dry gelatin in a test tube and 
moisten it with a single drop of concentrated nitric acid. 
Warm the mixture gently. What color is produced? Now add 
ammonia solution until the mixture smells of the ammonia. What 
has happened to the color just observed? Care should be used to 
prevent any nitric acid from getting on the skin for it produces a 
disagreeable stain. Why? 

385. The Protein Foods Absolutely Necessary. — While 
the protein foods yield energy equal in amounts to equal 
weights of carbohydrates, their chief value to the body lies in 
the fact that they alone contain nitrogen. Proteins must be 
found in every diet. The body may obtain energy quite as 
well from fat and carbohydrates as from protein, but neither 
fats nor carbohj^drates can furnish the body with the nitrogen 
which it needs. Moreover, the protein foods, as a rule, are 
higher in price than either the carbohydrates or the fats. It 
would be folly therefore to consume protein foods for the 
sole purpose of producing energy for the body when this 
energy can be obtained more cheaply from carbohydrates and 
fats. Moreover, the waste products from protein are much 
harder to get rid of than the waste products from carbohy- 
drates and fats. However, enough protein must be supplied 
the body at all times to keep the body in repair. 



332 FOOD— ITS USES AND PREPARATION 

386. How Much Protein? — This is a matter which has 
caused a great deal of discussion. But authorities are now 
agreed that the body should be supplied with from 3 to 5.3 
oz. of protein per day. Dr. Atwater gave the following as the 
protein requirement of persons engaged in different occu- 
pations : 

Man with hard muscular work 5.3 oz. per day 

Man with moderately active muscular work 4.4 oz. per day 

Man at sedentary or woman with moderately ac- 
tive work 3.5 oz. per day 

Man without muscular exercise or woman at light 

to moderate work 3.17 oz. per day 





Fig. 208. — Composition of the 
whole egg. 



Fig. 209. 



-Composition of whole 
milk. 



Exercise 72. — Weighing the Amount of Protein Needed by the 
Body for a Day 

Weigh a dozen eggs and calculate the average weight of one egg. 
By the use of Table VII on page 333 or Fig. 208 which gives the 
percentage of protein in whole eggs, calculate the weight of egg 
needed to furnish protein enough for a man of sedentary occupation. 
How many eggs will be required per day if eggs are to furnish the 
protein for the body? Weigh a quart of whole milk and by use of 
Table VII or Fig. 209 calculate the weight of milk a man would 
have to consume daily to furnish 3.5 oz. of protein. Calculate the 
weight of round steak needed to furnish 3.5 oz. of protein. 



THE DIET 



333 



Table VII. — Composition and Calorific Value of Foods 
(1) Cereals and Cereal Products 



Kind of Food 


Per cent. 

of 

water 


Per cent. 

of 
protein 

9.2 

9.2 
10.1 
16.7 

8.0 

6.8 
11.4 
10.5 


Per cent, 
of 
fat 


Per cent, 
of carbo- 
hydrate 


Heat 
value in 
greater 
calories 

per lb. 




35.3 

12.5 

7.3 

7.7 

12.3 

12.9 

12.0 

9.0 


1.3 
1.9 
1.8 
7.3 
0.3 
0.9 
1.0 
1.4 


53.1 
75.4 
78.4 
66.2 
79.0 
78.7 
75.1 
77.3 


1200 




1635 




1680 




1800 




1620 




1620 




1640 




1650 







(2) Eggs and 


Dairy Products 








65.5 
86.3 
50.0 
87.1 
90.5 
12. C 
34.2 


13.1 

12.8 

16.0 

3.2 

3.4 

0.5 

25.9 


9.3 

0.4 

33.0 

4.0 

0.3 

85.0 

. 33.7 


None 

None 

None 

5.0 

5.1 

None 

2.4 


635 


Eggs, white 


250 
1705 


Milk, whole 


325 
165 


Butter 


3600 


Cheese, full cream 


1885 



(3) Meats, Edible Portion 



Beef, chuck ribs 

Beef, loin 

Beef, round 

Beef, rump 

Beef, dried 

Pork, bacon, smoked . 
Pork, ham, smoked . , 
Pork, shoulder, fresh 
Poultry, chicken 

Poultry, turkey 

Fish, mackerel 

Fish, salmon 

Fish, sardines ...... 

Fish, trout, brook . . . 
Oysters, solids 



57.3 
60.5 
65.8 
56.7 
50.8 
18.2 
40.7 
57.5 
74.2 
55.5 
73.4 
69.1 
56.4 
77.8 



17.4 
18.3 
19.7 
16.8 
31.8 
10.0 
15.5 
15.6 
22.8 
20.6 
18.2 
18.2 
25.3 
18.9 
6.1 



24.4 
20.2 
13.5 
25.6 

6.8 
67.2 
39.1 
26.1 

1.8 
22.9 

7.1 
11.4 
12.7 

2.1 

1.4 



None 
None 
None 
None 
None 
None 
None 
None 
None 
None 
None 
None 
None 
None 
None 



1355 
1190 

935 
1395 

845 
3020 
1940 
1390 

500 
1350 

640 

820 
1010 

440 

235 



(4) Fruits and Fruit Products, Edible Portion 



Apples 

Bananas 

Blackberries 

Figs, drier 

Dates, dried 

Grapes , 

Oranges 

Peaches, fresh 

Raisins 

Raspberries, black 
Strawberries .... 
"Watermelon 



84.9 
76.1 
86.8 
21.2 
16.7 
77.9 
79.4 
89.8 
18.0 
84.7 
91.0 
92.7 



0.4 
1.3 
1.3 
4.3 
2.1 
1.3 
0.8 
0.7 
2.6 
1.7 
1.0 
0.4 



0.5 
0.6 
1.0 
0.3 
2.8 
1.6 
0.2 
0.1 
3 3 
1.0 
0.6 
0.2 



14.2 

22.0 

10.9 

74.2 

78.4 

19.2 

11.6 

9.4 

76.1 

12.6 

7.4 

6.7 



285 

447 

262 

1437 

1575 

437 

233 

188 

1562 

300 

169 

136 



(5) Miscellaneous, Edible Portion 



Beans, dry lima . . 
Potatoes, white . . 
Sugar, granulated 
Peanut butter . . . 



14.5 
79.S 
None 
11.2 



18.1 

2.2 

None 

25.8 



1.5 

0.1 

None 
38.6 



65.9 

18.4 

100.0 

24.4 



1586 

378 

1815 

2490 



334 FOOD— ITS USES AND PREPARATION 

387. How Much Food? — The food eaten must not only 
supply protein to keep the body in repair, but it must also 
furnish enough energy for the needs of the body. The ability 
of foods to produce energy in the body is measured by the 
amount of heat they produce when burned. Now the energy 
requirements of the body are measured in heat units, usually 
the greater calorie (Art. 102). Dr. Atwater in Farmer's 
Bulletin No. 142, U. S. Department of Agriculture, gave the 
following as the energy requirements per day for persons in 
different occupations: 

Man with hard muscular work 4150 greater calories 

Man with moderately active muscular work. . 3400 greater calories 
Man at sedentary or woman with moderately 

active work 2700 greater calories 

Man without muscular exercise or woman at 

light to moderate work 2450 greater calories 

Chemists have analyzed nearly every food, and have deter- 
mined its heat-producing ability by burning in a calorimeter. 
The results of these investigations on some of the common 
foods are given (page 333). By reference to Table VII, it is 
an easy matter to see just what food principles each food 
furnishes the body, what proportion of the food principles 
is furnished, and just how much energy, measured in greater 
calories, is furnished. 

388. Some Observations on the Table. — It is evident to 
anyone who will study the table that some of our foods contain 
much water. Their calorific value is, therefore, rather low. 
Watermelon, for instance, contains over 92 per cent, water 
and its heat value is but 136 Cal. per lb. while butter contains 
about 13 per cent, water and its calorific value- is 3600 Cal. 
per lb. This must mean that butter is a much better fuel for 
the body than watermelon. A man could scarcely eat enough 
watermelon to supply the energy needs of his body, while a 
rather small amount of butter would meet the energy demands 
easily (Fig. 210). 

It is also evident that some foods are much richer in certain 



THE DIET 335 

of the food principles than others. Thus butter contains 
about 85 per cent, fat and no carbo- 
hydrates while sugar contains 100 per 
cent, carbohydrate and no fat. The ce- 
reals are all rich in carbohydrate while 
their fat and protein percentages are 
rather low. The meats, on the other 

hand, contain, as a rule, no carbohy- FlQ - 210.— Composi- 
' ' ' tion of butter. 

drates while their percentages of fat 

and protein are rather high. In general fruits contain much 
water, little protein and fat, and relatively much carbohy- 
drate. In selecting foods, then, a knowledge of their com- 
position is necessary. 

389. The Heat Value of the Food Principles. — When the 
pure food principles are burned in the calorimeter it is found 
that they produce the following amounts of heat : 

Protein 2562 greater calories per pound 

Carbohydrate 1860 greater calories per pound 

Fat 4286 greater calories per pound 

But the body does not realize the full heat value of the food 
principles when they are oxidized in the body. This is be- 
cause of incomplete digestion and incomplete oxidation. The 
following is the net value in heat units of above to the body : 

Protein 1815 greater calories per pound 

Carbohydrate 1815 greater calories per pound 

Fat 4084 greater calories per pound 

It will thus be observed that protein and carbohydrates are 
of equal value to the body as producers of energy, while fat 
produces about 2% times as much energy. It is a well-known 
fact that fatty foods are greater heat producers than other 
kinds. Inhabitants of cold climates consume and relish large 
quantities of fat. Most of us have a better appetite for fat 
in the winter than in the summer. Why ? 

390. Bread and Butter ; Pork and Beans. — These are well- 
known combinations of food. Why are these foods thus com- 



336 



FOOD— ITS USES AND PREPARATION 



bined? It will be observed that bread is composed of 9.2 
per cent, protein, 1.3 per cent, fat, and 53.1 per cent, carbo- 
hydrate. It is therefore rather poor in fat. Butter on the 
other hand is rich in fat, so that a thin coat of butter on a 
slice of bread supplies the deficiency of fat in the bread. Ex- 
plain why the combination of fat pork and beans is better 
than either one alone. What combination would you suggest 
with eggs ? Why do we relish cheese with bread or crackers ? 
Why do we combine meat and potatoes ? Why combine milk, 
eggs, and sugar in a custard ? 



Table VIII. — One Hundred Calorie Portions op Foods 



Kind of Food 

Bread, wheat 

Corn Flakes, toasted 
Oat meal, uncooked . 
Wheat, shredded . . . 

Eggs, whole 

Milk, whole 

Butter 

Cheese 

Round steak 

Bacon 

Ham, smoked 

Chicken, dressed . . . 

Fish, trout 

Apple 

Raisins 

Beans, dry lima 

Potatoes 

Sugar, granulated . . . 



Weight of Food 
Yielding 
100 Calories 


Weight of Protein 

in 100 Calorie 

Portion 


1.33 


ounces 


.122 


ounces 


.95 


ounces 


.095 


ounces 


.88 


ounces 


.147 


ounces 


.97 


ounces 


.102 


ounces 


2.52 


ounces 


.330 


ounces 


4.92 


ounces 


.157 


ounces 


.44 


ounces 


.002 


ounces 


.85 


ounces 


.220 


ounces 


1.71 


ounces 


.337 


ounces 


.53 


ounces 


.053 


ounces 


.82 


ounces 


.127 


ounces 


3.20 


ounces 


.729 


ounces 


3.63 


ounces 


.686 


ounces 


5.61 


ounces 


.022 


ounces 


1.02 


ounces 


.026 


ounces 


1.00 


ounces 


.181 


ounces 


1.20 


ounces 


.092 


ounces 


.88 


ounces 


none 





391. Food for a Day. — What amount of food should be pur- 
chased at the market in order to properly nourish a man 
engaged in ordinary labor? Bearing in mind that a man en- 
gaged in moderately active muscular work should have food 
enough to furnish about 3400 calories per day (Art. 387) 
and that he should have about 4.4 ounces of protein per day 



THE DIET 



337 



(Art. 386) it becomes a simple problem to calculate bis food 
requirements by making use of Table VIII. The figures re- 
sulting from such calculations are shown in the following 
table. 

Table IX. — Food for a Day for Man at Moderate Labor 



Kind 
of 
Food 


Am 
Weight or 
Volume 


ount in 

100-Cal. 
Portions 


Total No. 
of Cals. 
Yielded 


Protein 

in 
Ounces 




13.3 oz. 
1.75 oz. 

1 pint 

2.5 oz. 

1.0 oz. 

5.0 oz. 

2.0 oz. 
1.75 lb. 
1.75 oz. 


10 100-Cal. 

2 100-Cal. 
3.2 100-Cal. 

3 100-Cal. 
2.25 100-Cal. 

3 100-Cal. 

4 100-Cal. 
5 100-Cal. 
2 100-Cal. 


1,000 Cal. 
200 Cal. 
320 Cal. 
300 Cal. 
225 Cal. 
300 Cal. 
400 Cal. 
500 Cal. 
200 Cal. 




Oat Meal 


30 oz. 


Milk 




Cheese 


.66 oz. 


Butter 




Round steak 


1.00 oz. 


Bacon 


.21 oz. 


Potatoes 


.46 oz. 


Sugar 








Total | 


3,400 Cal. 


4.35 oz. 



In making up such a menu one should expect to get nearly 
one third of the total calories from bread which will furnish 
nearly one fourth of the total weight of protein. Potatoes 
and sugar, together, may furnish about one fifth of the cal- 
ories and one tenth of the protein. The remainder of the 
calories and protein required may be obtained from such 
foods as butter, cheese, meat and cereal. 



PROBLEMS 

1. Make up a breakfast menu for a man engaged in moderate labor 
so that he may obtain one third of his daily requirement from the 
meal. 

2. Arrange a full meal menu for a man at moderate labor so as 
to provide one half of his dairy requirement. 

392. The Results of Eating too Much. — Many people con- 
sume more food than the body needs. No good can come from 



338 FOOD— ITS USES AND PREPARATION 

such a practice. The food in excess of 3500 or 4000 Cal. per 
day is not only unnecessary, but more than this, it interferes 
with the proper working of the body. The organs of excretion 
have an added and useless burden placed upon them. Physi- 
cians tell us to eat slowly, to chew the food until it becomes 
creamy in the mouth, and to let the act of swallowing be 
largely involuntary. By following this plan, the appetite is 
satisfied with less food and the danger of overeating is dimin- 
ished. Half an hour should be used in eating a meal. The 
food should not be washed down, improperly chewed, by use 
of large draughts of water. 

Many people partake too liberally of a protein diet. Hav- 
ing an appetite for meats and similar high protein foods they 
eat this kind to the exclusion of foods containing more car- 
bohydrate as bread. This is especially likely to happen when 
one is ordering food from an extensive menu. Unless care 
is exercised a selection is likely to be made which is too high 
in protein. 

II. PROCESSING FOOD 

393. Origin of Processing. — Early races learned arts of 
processing foods whereby they might be preserved from the 
season of plenty to a season of scarcity. Thus man learned 
to dry fruits, to cure meat by salting, drying, and smoking, 
and in very recent times to preserve fruits and vegetables by 
canning. He also learned processes whereby the work of con- 
centrating the food stuff with reference to certain constituents 
might be done. Thus from milk, cheese, rich in fat and pro- 
tein, is made by processing milk. Similarly butter is ex- 
tracted from milk; lard and tallow from animal bodies; 
starch from corn, potatoes, and rice ; flour from wheat ; sugar 
from the cane, beet, and maple ; and oils from the olive, corn, 
and cottonseed. 

Great industries concerned with the business of processing 



PROCESSING FOOD 339 

food have arisen in our country. It seemed at one time that 
the great meat packing concerns, by extending their activities 
to other lines than the meat foods would soon come to control 
the food markets of the country. But late in 1919, under 
pressure from the Federal government they relinquished their 
hold on other lines and agreed to confine their activities to 
meat foods. 

The Dairy Products 

394. Milk. — Milk is the food of the infant for the early 
months of his life. It contains all of the ingredients needed 
for the child. It is also largely used as food by adults. Milk 
should not be looked upon as a mere beverage. Its food 
value should be taken into account in the dietary. Milk is 
especially liable to become impure through the introduction 
of filth and germs in the dairy. It is an ideal breeding ground 
for bacteria and its production and handling should be done 
under the most sanitary conditions possible. Because milk 
contains so large a proportion of water (87 per cent.) it is 
sometimes made a more concentrated food by removal of a 
part of the water by evaporation. The resulting product, 
condensed milk, is sterilized and sealed in air-tight cans 
when it can be kept for a long time in a usable condition. 
Condensed milk contains about 27 per cent, of water. Often 
considerable sugar is added during the condensing process. 
Sometimes all of the water is evaporated from milk and the 
resulting milk powder is used in the preparation of self -rising 
pancake flour. When water is added to the flour, the milk 
powder dissolves and the result is much the same as that ob- 
tained by adding milk to the flour. Condensed milk is used 
in the preparation of ice cream and candies. 

395. The Percentage of Fat in Milk.— Whole milk ordina- 
rily contains from 3 to 5 per cent. fat. Cream contains from 
18 to 45 per cent. fat. Much attention is given to the amount 
of fat in milk, and it is commonly supposed to be a safe guide 



340 



FOOD— ITS USES AND PREPAKATION 



in judging the quality of the milk. But it must be remem- 
bered that there are other food materials in milk besides fat. 
Milk also contains about 3.2 per cent, protein and 5 per cent, 
carbohydrate, milk sugar (see Fig. 210). But in general, if 
the fat percentage is low, the other constituents are likely 
to be low also. But there is much food value in skim milk. 
Skim milk contains the valuable protein. One might pur- 




17 SCC Graduato fbr 
176 CC Pipette fo y t Mllk Boifie tulphunc acid 

Fig. 211.— Glassware for the Babcock Milk Test. 



chase skim milk and make up for the fat it lacks by purchas- 
ing a cheaper fat as oleomargarine. Most states and cities 
have laws fixing the lowest amount of fat that milk can con- 
tain tp be sold as whole milk. These laws usually place the 
lowest limit at 3 per cent, or 3.5 per cent. fat. 

396. The Babcock Method of Determining Fat in Milk. — 
The method of the test is as follows: A certain amount* of 
milk is placed in a test bottle having a graduated neck. Con- 
centrated sulphuric acid is then added to the milk and the 
mixture is well shaken. The sulphuric acid dissolves all of 



PROCESSING FOOD 



341 



the constituents of the milk except the fat. The bottle and 
the mixture are then placed in the Babcock machine in which 
they are whirled at a high rate of speed. The fat, being the 
lighter, rises to the surface of the mixture in the bottle and by 
getting the fat into the graduated neck the percentage of fat 
may be read directly. 



Exercise 73. — The Babcock Test 

(1) Mix the milk to be tested by pouring it from one bottle to 
another several times. This mixes the cream with the remainder 
of the milk. (2) By means of a milk pipette (Fig. 211) draw 
out 17.6 c.c. of the mixed milk and place it in an 8- or 10-per cent. 

milk bottle (Fig. 211). Do not 
insert the tip of the pipette so far 
into the milk bottle that the milk 
is spilled as the air escapes from 
the bottle. Draw out another 17.6 
c.c. portion and place it in 
another bottle. (3) Place 17.5 
B.C. of concentrated sulphuric acid 
in the acid measure (Fig. 211) 
using care to avoid spilling any of 
the acid on the hands or clothing. 
Now carefully pour the con- 

Fig. 212.-The centrifuge ma- C f ntl ' ated 11 aeid into the test bot " 
chine. tie of milk containing the 17.6 c.c. 

of milk allowing the acid to run to the bottom of the bottle. Do 
not shake the aeid and milk until the other bottle is prepared. 
Measure another 17.5 c.c. portion of the acid and pour it into the 
second bottle of measured milk. (4) Now carefully shake the bot- 
tles containing the milk and acid so as to mix thoroughly. Do not 
try to mix the liquids by placing the finger over the mouth of the 
test bottle or the finger will be burned. In shaking, be careful that 
the curd does not become lodged in the neck of the bottle. The 
mixture becomes very hot and it is to be kept hot during the entire 
test from this point on. The acid has now dissolved all of the 
constituents in the milk except the fat. The fat is now to be sepa- 
rated by use of the machine. (5) Have about a pint of water 
heating so it will be ready for use later on. (6) Place the test 
bottles at opposite points in the centrifuge machine (Fig 212) and 




342 FOOD— ITS USES AND PREPARATION 

place bottles filled- with water in the other holders so as to balance 
the machine. Turn the handle of the machine at the rate of about 
70 revolutions per minute for five minutes. Remove the test bottles 
and carefully fill them with boiling water until the liquid comes' 
up near the top of the neck of the bottle. Be careful to avoid 
pouring in so much water that the fat runs out of the bottle. Re- 
turn the bottles to the machine and whirl them for one minute more 
at the same rate as indicated above. By this process, the fat is all 
thrown into the graduated neck of the bottle where its amount 
may be read. (7) Read the upper and the lower limits of fat 
column in the neck of the bottles. Subtract the smaller reading 
from the larger one. The difference is the percentage of fat in the 
milk. Repeat the operation with the other bottle. Do the two per- 
centages of fat agree? 

PROBLEM 

How many pounds of butter could be made from 100 lb. of the 
milk tested, provided the butter is to contain 85 per cent, fat, 13 
per cent, water, and 2 per cent, salt? 

If possible, test for fat by the Babcock method to see how com- 
pletely the fat has been removed, milk that has been skimmed by 
hand. Also test milk that has been separated by means of a cream 
separator (see Art. 543). For accurate work on the latter kind of 
milk, a skim-milk bottle should be used. 

397. Butter. — When cream is allowed to* " ripen" (Art. 
544) and is then agitated in a churn the fat gathers 
together in masses known as butter. These masses of butter 
are gathered together, washed with water, worked to remove 
the excess of water, and then salted to impart an agreeable 
flavor. Churning is most quickly accomplished by having the 
temperature of the cream about 65 or 70°F., but more solid 
butter, and butter of better grain or texture is obtained by 
churning at a lower temperature. The composition of butter 
is show T n in Table VII. According to a standard established 
by Congress, butter for interstate traffic must not contain 
more than 16 per cent, of water nor less than 82.5 per cent, of 
fat (see Fig. 210). 

398. Renovated or Process Butter. — Through careless 



PROCESSING FOOD 



343 



methods of handling milk and cream and carelessness in manu- 
facturing butter, it sometimes happens that the butter is of 
inferior grade. Moreover, it may be held so long that it has 
become rancid and unfit for food. Such butter is renovated 
in specially constructed factories. The butter is melted and 
air is blown through the melted fat. This removes the dis- 
agreeable odors. The salt and many undesirable materials in 
the butter sink to the bottom of the vessel containing the 
melted fat. The purified fat is then drawn off and mixed with 




Fig. 213. — Ripeners for oleomargarine. 

sweet milk, then it is churned, much as cream is churned. 
The product is sweet and resembles true butter in many re- 
spects. The manufacture and sale of renovated, or process 
butter, is regulated by law. The law intends that the pur- 
chaser shall know that he is buying such an article and not 
true butter. All renovated butter must be properly labeled. 
399. Butterine, or Oleomargarine. — Because of the high 
price of butter fat, various cheaper fats are sometimes used 
for the manufacture of substitutes for butter. These substi- 
tutes are called butterine, or oleomargerine. Butterine is 



344 



FOOD— ITS USES AND PREPARATION 



a healthful and nutritious food and may be used instead of 
butter in the diet. Good butterine is better than poor butter. 
Because unscrupulous manufacturers and dealers in but- 
terine have tried to sell their product as butter, the manu- 
facture and sale of butterine is surrounded by many legal re- 
strictions. Many grades of butterine are manufactured. In 
the best grades a considerable quantity of butter fat is used 
to impart a flavor of real butter to the product. In the 
cheaper grades very little butter fat is used. The fats used 




Fig. 214. — Churning oleomargarine. 



as substitutes for butter fat in butterine come from animals 
and from the cotton seed. One of the substituted fats is 
called neutral. Neutral is made from the leaf lard of hogs 
by rendering (trying out) the material at a very low tempera- 
ture and then expressing (pressing out) the liquid fat from 
the tissues. It is without odor and taste. Another sub- 
stituted fat is called oleo oil. This oil is expressed from the 
fat of cattle. These animal oils are prepared from animals 
which have been inspected by United States inspectors and 



PROCESSING FOOD 345 

passed. They are prepared in a sanitary manner and are 
wholesome articles of food (Art. 405). Cotton seed oil 
products (Art. 407) are sometimes used in butterine in addi- 
tion to the fats mentioned. Such amounts of these fats are 
used as will give with the butter fat a mixture resembling 
true butter. The cream in the milk is ripened (Fig. 213 as 
for the ordinary methods of churning. The proper amounts 
of neutral, oleo oil, and cotton seed oil product are then mixed 
with the ripened cream and the mixture is churned (Fig. 




Fig. 215. — Working oleomargarine. 

214. The fats gather much as true butter gathers. They 
are removed from the milk and worked and salted as in the 
<?ase of butter (Fig. 215). Uncolored butterine is taxed *4 
ct. per lb. If the butterine is colored so that it resembles 
"butter, an additional tax of 10 cts. per lb. is levied by the 
Federal government. 

Exercise 74. — The Foam Test for Butterine and Butter 
Place a lump of butterine in a tablespoon and heat it over a 
flame until it melts (Fig. 216). Continue the heating, noticing the 



346 



FOOD— ITS USES AND PREPARATION 



absence of foam and sputtering. Now treat a lump of butter in 
like manner and notice the foaming and sputtering which accom- 
pany the escape of water from the butter. By this test, it is easy 
to distinguish butterine and butter. If obtainable, test some reno- 
vated butter in the same manner. Renovated butter behaves in a 
manner similar to that of butterine. 



400. Cheese. — Both cheese and butter have been used by 
pastoral people for ages. Abraham set butter and milk before 
his guests. When a lad, David was sent by his father with 
cheeses for the captain of the company in which his brothers 
were serving in the army of Israel. Cheese is the fermented 
curd of milk. When milk sours, the casein (curd) of the 




Fig. 216.— 
Foam test for 
butterine and 
butter. 



Fig. 217. — Composition, 
of cheese. 



milk separates from the watery portion called the whey. 
The curd contains nearly all of the food substance in the 
milk except the sugar. The curd may also be produced by 
adding rennet to the milk. Rennet is extracted from the 
stomachs of calves. The curd is separated from the whey 
and then pressed to remove as much of the fluid substance as 
possible. The pressed material is then allowed to ripen in a 
properly prepared room. During the ripening process the 
different constituents of the curd undergo certain chemical 
changes, largely caused by bacteria, producing the flavor and 
odor of cheese. If the cheese is made from whole milk the 
product is called full cream cheese. The composition of this 
kind of cheese is given in Table VII. It will be noticed that 



PROCESSING FOOD 347 

cheese still contains a considerable amount of water but much 
less than whole milk (Fig. 216) . In a sense, then, cheese may 
be looked upon as a kind of condensed-milk product. In some 
cases, the valuable milk fat is removed from the milk before 
making cheese. In this case cheaper animal or vegetable fats, 
as neutral and cotton seed oil products, are put in to com- 
pensate for the milk fat removed. Such cheese is known as 
filled cheese. Its manufacture is regulated by law as in 
the case of butterine, and the consumer is supposed to be 
informed that he is buying filled and not full cream cheese. 
"When good fats are used as substitutes for the milk fat, 
filled cheese is wholesome and nutritious. 

Meat Foods 

401. Importance of Meat in the Diet. — Meats are eaten for 
the protein and fat which they contain. As we have seen, fat 
is useful to the body as a producer of energy, while protein is 
needed for its nitrogen. That protein may be obtained from 
vegetable substances there can be no doubt. Some people 
eat no meat whatever, obtaining all their protein and fat 
from vegetable substances. It is a much debated question 
whether we can get along just as well without meat. But 
there can be very little question whether, as a nation, we do 
not eat too much meat. It is doubtless true that most of us 
could get along quite as well if we were to eat less meat and 
more vegetable foods, such as grains and vegetables. 

402. Meat Rapidly Deteriorates When Stored. — The fat 
and protein compounds of meat rapidly undergo changes when 
they are kept. On the other hand, the food substance stored 
in the grains may be kept for a considerable length of time 
without damage. For this reason meats must be consumed 
soon after the animals are slaughtered. In order to prevent 
decay several methods are used. 

403. Preserving Meat by Cold Storage. — When the freshly 
prepared meat is placed in cold storage the rate of decay is 
greatly lessened. However, changes do take place in the 



348 FOOD— ITS USES AND PREPARATION 

meat, rendering it less fit for food. Refrigeration during 
shipment is very useful as a means of transporting meat from 
the packer to the dealer and to the consumer. Fresh meat 
should not be exposed for sale in the open air. It should be 
kept cool and free from dirt until it reaches the consumer. By- 
freezing fresh meat it has been possible to preserve it for 
months with apparently very little change in the product. 
But the aim should not be to see how long meat may be kept, 
but rather to deliver it to the consumer as soon as possible after 
the animal is killed. 

404. Preservation of Meat by Use of Salt and Other 
Chemicals. — When fresh meat is immersed in a strong brine, 
the meat is preserved from decay. Such treatment is known. 
as pickling. Often other preservatives than salt are used. 
Saltpeter is often employed. It is not known that salt and 
saltpeter injure the meat in any way. But other and poison- 
ous materials are sometimes used. These include borax, boric 
acid, sulphurous acid, and sulphites. They are powerful 
preservatives, and when taken in large amounts with the food 
are injurious to the health. Sulphurous acid and sulphites 
also impart a red color to the meat, thus causing it to appear 
fresh. Chopped meats are often treated with sulphites to 
prevent decay and to keep the meat red. Many states have 
laws which limit the amount of such preservatives that may 
be used and also provide that the purchaser shall be informed 
of the presence of the chemical in the meat. In this latter 
respect the law is often disobeyed. 

405. Meat Inspection. — At all establishments at which 
animals are slaughtered for food which is to be shipped from 
one state to another, the United States Government stations 
officers whose duty it is to inspect all animals that are to be 
slaughtered and also to inspect the meat produced to see that 
it is fit for human food. Diseased animals are condemned 
and destroyed so as not to be used for food purposes. Food 
that is passed by the inspectors is marked "U. S. Inspected 



PROCESSING FOOD 349 

and Passed." The United States inspectors work in con- 
junction with state and city food inspectors and thus largely 
prevent the coming on the market of meat unfit for human 
consumption. 

406. Lard and Lard Substitutes. — When the fat of the hog 
is rendered, lard is obtained. Because of its rather high 
price lard is frequently adulterated with cheaper fats, beef 
tallow and cotton seed oil being used for the purpose. Such 
mixtures are highly nutritious. They must be sold, however, 
as a compound lard. 

407. Cotton Seed Oil. — Since cotton seed oil has been 
mentioned so frequently in the foregoing discussion, it is 
proper that it should be discussed here, although it is a vege- 
table and not an animal product. The seed of the cotton 
plant is rich in fat. For each bale of cotton weighing 500 lbs., 
about 1000 lb. of seed are produced. About 6,000,000 tons 
of cotton seed are produced annually in the United States, 
two-thirds of which is worked to produce oil. This gives an 
annual production of about 125,000,000 gals, of oil, more than 
1 gal. per capita. After the cotton lint has been removed 
from the seeds, the hulls are taken off and the pulp pressed 
to liberate the oil. The oil is further refined and finds use 
in butter and lard substitutes, as a salad oil, in packing sar- 
dines, and in soap making. The pulp from which about 85 
per cent, of the oil has been expressed is then broken into small 
pieces and used as stock feed. The use of this vegetable oil 
takes the place of much animal fat. Its nutritive value is 
equal to that of the animal fats. 

The Cereal Foods 

408. The Cereals That are Used for Food. — Wheat, corn, 
oats, rye, rice, barley, and buckwheat are commonly used as 
foods. The cereals contain large amounts of starch and 
smaller amounts of fat and protein. They are the chief 
sources of the starchy foods, and for great numbers of the 



350 FOOD— ITS USES AND PREPARATION 

human race they furnish the chief source of protein. The 
use of the cereals as food will doubtless increase in importance 
as meats become less abundant and higher in price. 

409. Wheat. — This is the cereal that is most extensively 
used as human food. It grows in many parts of the world. 
In North America, wheat is known as winter or spring 
wheat according to whether it is sowed in the fall and allowed 
to lie in the field through the winter or whether it is sowed 
in the spring of the year in which it is to be harvested. Win- 
ter wheat can not be grown in the northern climates because 
of the cold winters. These regions grow only spring wheat. 
This cereal is rich in protein, containing about 12 or 13 per 
cent. It is poor in fat, but rich in carbohydrate. 

410. Wheat Flour. — The wheat is ground between revolving 
rollers to extreme fineness. The ground material is then 
sifted through very fine bolting cloth which grades the ground 
material into several grades. These grades may be classified 
as patent flour, baker 's flour, and low-grade flour. Be- 
sides these different grades of flour the wheat also produces 
bran, shorts, and screenings. To produce a 48-lb. sack of 
patent flour requires nearly 83 lb. of wheat, or about 1.4 bu. 
Besides the patent flour, about 9.3 lb. of baker's flour and 5.6 
lb. of low-grade flour are produced. The remainder of the 83 
lb. of wheat appears as bran, shorts, screenings and waste. 

411. Graham Flour. — True graham flour is made by 
grinding the entire grain without bolting. It, therefore, has 
the same composition as wheat. Most of the graham flour 
that is produced at present is bolted, so that much of the bran 
covering of the grain is removed. 

412. Whole or Entire Wheat Flour. — This name is applied 
to a flour produced by removing the bran covering of the 
grain and grinding. It, therefore, has about the same com- 
position as the so-called graham flour. 

413. Gluten. — Gluten is the name given to two of the 
important proteins in flour. It is the material which gives to 
the flour its sticky character when wet. Without the gluten 



PROCESSING FOOD 351 

in the flour, bread, as we know it, could not be made. The 
gluten is insoluble in water and helps the flour to make a 
dough when wet. The starch and fat in the flour may be 
washed away from the gluten. 

414. Shredded Wheat. — This is a whole wheat preparation, 
cooked and ready to serve. It is one of the common wheat 
breakfast foods. The wheat is thoroughly cleaned and is then 
steam cooked until soft. The excess of water is then dried 
from the wheat and it is put into machines which crush the 
grains and form them into shreds which are delivered to an 
endless belt. The shreds are here cut into lengths to form the 
biscuits. These biscuits are then placed on trays and baked 
in electric ovens. Subsequently the crisp biscuits are packed 
in cartons and sealed. The wheat food is made light entirely 
by mechanical means, no yeast or other leaven being used in 
the process. The finished product has nearly the same com- 
position as the wheat from which it is made. 

415. Corn — Its Use as Human Food. — This cereal is more 
largely produced in the United States than is wheat. Corn 
contains the same food principles as wheat does. It con- 
tains more fat, however, and somewhat less protein. The 
proteins of corn do not include very much gluten. For this 
reason, corn flour has not been used to a very great extent, 
even in the United States, for bread. Moreover, the high per- 
centage of fat in whole corn meal causes the meal or flour to 
become rancid in warm weather and hence unfit for food. Be- 
sides the corn consumed as flour, there is much of it worked 
up into breakfast foods, while a still larger part of the grain 
is carried through various chemical transformations for the 
making of starch, corn syrup, alcohol, and vinegar. There is 
every reason for believing that corn food products will be 
more extensively used in the future. But by far the largest 
part of the corn crop of this country is now consumed on the 
farm as stock feed. From it, are produced the various ani- 
mal products so useful to man, including beef, pork, and dairy 
products. Food for man thus produced indirectly from corn, 



352 FOOD— ITS USES AND PREPARATION 

is much more expensive than when corn is used directly as 
food. 

416. Corn Flakes. — The well-known corn flakes represent a 
successful attempt to produce a food from corn which is at 
once palatable and nutritious. The operation of making corn 
flakes begins with the hominy, or corn grit, mills which are 
usually located in the "Corn Belt" of our country. Here 
the shelled corn is steeped in water until it is soft. It is then 
put through mills which loosen the germ and the skin which 
are removed from the remainder of the grain. The germ con- 
tains nearly all of the fat of the grain and much of the pro- 
tein. The germs and skins are made into cattle feed, much 
being consumed on dairy farms. The remainder of the grain 
constitutes the hominy. The hominy, or grits, are dried and 
shipped to the flaking mill. Here the grits are steam cooked 
until soft; then the cooked material is put through flaking 
machines which convert the grits into flakes as thin as paper. 
The flakes are then toasted in great gas-heated ovens and 
packed in air-tight packages while crisp. In this condition 
they are delivered to the consumer. Large quantities of corn 
are thus flaked and find their way to the breakfast tables of 
American homes. 

417. Corn Starch. — Most of the starch used in the United 
States is prepared from corn, although wheat and potatoes are 
also used to a limited extent. In Europe the potato is exten- 
sively used. Corn contains about 55 per cent, starch, while 
the potato contains about 18 per cent. However, an acre of 
land in Europe planted to potatoes can be made to yield a 
larger amount of starch than an acre of corn. About 50,000,- 
000 bu. of corn are annually converted into starch and allied 
products in the United States, which represents, however, but 
one-fiftieth of the annual production. 

418. Preparation of Corn Starch. — The shelled corn is 
steeped for three or four days in great tanks containing water 
and sulphur dioxid. This serves to loosen the skin and the 



PROCESSING FOOD 355 

germ. The soaked corn is then gently ground in mills which 
crush the grain, loosening the skin and germ from the part of 
the grain containing most of the starch. The ground material 
is then placed in tanks containing water in which the germs 
float because of the oil which they contain while the starch 
and skins sink. The germs are dried, ground, and pressed in 
filter presses, thus removing the oil. Corn oil has many uses 
as human food. The cake remaining after removal of the oil 
is called oil cake. It is ground and largely used as stock 
feed. The starch and skins are re-ground and then put 
through the shakers which separate the starch from the skins. 
The skins, or bran, are again ground and again treated to 
remove the remainder of the starch. The starch suspended in 
water is then run into long troughs, inclined at a gentle slope. 
As the starch water flows through the troughs, the starch 
settles, while the gluten and water flow out at the end of the 
trough. The gluten is removed from the water, dried, ground, 
and marketed as gluten meal which is used for stock feed. 
The accumulated starch in the troughs is removed, dried, 
pressed, and made into lump starch. The product still con- 
tains from 12 to 15 per cent, moisture. 

419. Glucose. — Much starch is converted into syrups and 
sugar known as glucose syrup, or corn syrup, and grape 
sugar. Corn syrup is very extensively used as a food. It 
is sweet, but less sweet than ordinary sugar. It is without 
flavor and consequently the table syrups are frequently pre- 
pared by blending corn syrup and cane sugar, or refiner's 
syrup, the latter imparting a pleasing flavor. A popular 
brand of corn syrup also contains vanilla flavor. 

Commercial glucose is composed of the following carbo- 
hydrates: dextrose; maltose; and dextrin. Dextrose is 
one of the constituents of honey; maltose, or malt sugar is 
formed when certain grains sprout; while dextrin is the ad- 
hesive commonly used on postage stamps. Each of these 
materials has a nutritive value equal to that of ordinary sugar. 



354 



FOOD— ITS USES AND PREPARATION 



These materials are prepared from starch by the action of 
dilute acids upon starch. 

420. Preparation and Uses of Glucose. — The starch used 
in the preparation of glucose is obtained as already described 
except that it is not dried after it has been collected in the 
troughs. The wet material "green starch" is mixed with 
water to make a thick, creamy liquid, and then it is mixed 
with the proper amount of hydrochloric acid for the change ; 



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jTjq 218. — Manufacture of glucose. Shows the tops of the copper 
converters and the working floor around them, also the neutralizers on 
the balcony just above and surrounding the converter floor. 

the mixture is then run into a converter where the trans- 
formation of starch into glucose takes place (Fig. 218). In 
the converter the mixture is subjected to a steam pressure of 
50 lbs. Under this pressure the temperature of the steam is 
about 150°C. or 300°F. Under these conditions the conver- 
sion is rapid. When the starch has disappeared, the liquid 
is blown by the steam pressure into the meutralizer (Fig. 
218) where soda is added to neutralize the acid used in the 
conversion. The neutralization forms salt as one product of 
the chemical reaction. The salt remains in solution in the glu- 
cose, but there is so little of it that it is not noticed in the final 



PROCESSING FOOD 355 

product. After neutralization the liquid, which is cloudy be- 
cause of impurities, is filtered, first, through great suspended 
bags called bag filters, then through bone char. Bone char, 
as its name indicates, is made by charring bones. When liquid 
is filtered through the bone char, the impurities are absorbed 
into the pores of the char while the clear liquid runs on 
through. The bone-char filters are great tanks filled with the 
char, and through the char, the liquid is forced. The glucose 
liquid comes from the filter, bright and clear, but much thinner 
than the syrup used on the table. The liquid is next concen- 
trated by evaporating a part of the water in evaporators. 
Here evaporation is carried on at a low temperature so as to 
prevent the darkening of the syrup. Evaporation at a low 
temperature is accomplished by reducing the pressure of the 
steam within the evaporator. After the required amount of 
evaporation, the liquid is placed in barrels and cans for de- 
livery to the consumer. Grape sugar is made by evaporating 
the syrup still further and subsequently crystallizing the 
sugar. 

Aside from its use as a table syrup, glucose is used in mak- 
ing jellies, preserves, and candy. Large quantities are used 
for the last-named purpose. Many medicines contain glucose 
syrup as body. 

421. Sugar. — Sugar is one of the most widely used foods. 
There are but few manufactured foods found in the markets 
which are as nearly pure as sugar. While the term "sugar" 
is usually taken to mean the common article of food of the 
table, it will be remembered that there are several kinds of 
sugar (Art. 382) . Sucrose is the sugar meant as we commonly 
use the term. Sucrose is found in nature in the sugar cane, in 
the sorghum plant, in the sugar beet, in the sugar maple, and 
in certain kinds of palms. When pure sucrose is obtained 
from any one of these sources it is found to be like that from 
any of the other sources. Pure sucrose from the cane is the 
same as that from the beet. There is a popular prejudice 
against beet sugar. Many people think it inferior to cane 



356 FOOD— ITS USES AND PREPARATION 

sugar. They are equally nutritious. Maple sugar is prized 
because of its peculiar flavor. But when maple sugar is en- 
tirely purified and its sucrose extracted it is the same as 
sucrose from the cane or the beet. Nearly all of the sugar of 
commerce is derived from the cane and the beet. The sugar 
beet grows in temperate climates while the cane is limited to 
the tropical or semi-tropical countries. 

422. Preparation of Sugar from Cane. — The sugar cane 
contains about 14.5 per cent, sucrose of which less than 90 per 
cent, is usually extracted. The cane is stripped of its leaves, 
cut, and carried to the mill where it is run between great rolls 
in which the cane is crushed and the juice containing the 
sugar is squeezed out. Water is applied to the crushed cane to 
remove more of the sugar. The crushed cane is finally burned 
beneath the boilers of the mill for the generation of steam for 
power. The juice is strained and then treated with lime. 
Upon being heated a scum arises on the juice. This scum is 
removed and the purified juice is then evaporated in vacuum 
evaporators as in the manufacture of glucose. The sugar solu- 
tion is evaporated until crystallization of sugar begins when 
it is run into tanks where it is stirred until the crystallization 
is complete. The crystals are then separated from the syrup 
or molasses. The latter finds extensive use in the baking in- 
dustry and in making stock feed. The sugar, known as raw 
sugar in commerce, is then shipped to the refinery to be con- 
verted into the article which we know. 

423. Preparation of Sugar from Beets. — Sugar beets con- 
tain from 14 to 17 per cent, sucrose. The beets are harvested 
and the tops removed. After being carried to the factory they 
are washed and sliced in thin slices. The sliced beets are 
placed in a series of great tanks called diffusers, which we 
shall call, in turn, A, B, C, D, and E. Fresh water is fed into 
top of A and as it passes down through the slices the sugar 
is extracted. Emerging from the bottom of A, the solution 
is next fed into the top of B. As it passes through the slices 
in B, it dissolves more sugar, but removes relatively less sugar 



PROCESSING FOOD 357 

than was removed in A. Thus the solution is led, in the same 
manner, through C, D, and E, each time becoming a more 
concentrated solution of sugar, but removing, relatively, less 
and less sugar from the slices in each difruser in turn. Fi- 
nally as it emerges from E, the solution is almost as concen- 
trated in sugar as is the natural juice contained in the slices 
in E. The solution is then purified and the sugar extracted. 

Meanwhile, the continuous passage of water through A has 
removed as much sugar from the slices as it is profitable to 
remove. The exhausted slices in A are then removed, and A 
is refilled with fresh slices and it is then placed next in series 
after E. Fresh water is then fed into B. From B the solu- 
tion passes in turn through C, B, E, and A. The solution 
from A is purified and the sugar extracted. Meanwhile the 
sugar has been quite completely removed from the slices in B. 
Its contents are emptied and it is refilled with fresh slices and 
placed next after A in series. Fresh water is then fed into 
C, passing, in turn, through D, E, A, and B. The solution 
from B is then purified and the sugar extracted. So the proc- 
ess is a continuous one. In this manner the maximum quan- 
tity of sugar is removed from the sliced beets by means of 
the minimum quantity of water. 

In beet sugar factories the raw sugar is refined in the one 
establishment, whereas cane sugar is usually refined in other 
factories than those that produce the raw sugar. 

424. Sugar Refining. — In the process of refining sugar, the 
raw sugar is dissolved in water and the syrup is then purified 
by means of lime and acid, after which the syrup is filtered 
through bag filters and then through bone char for clarifica- 
tion. The clarification is similar to that used in glucose. The 
purified syrup is then evaporated in vacuum evaporators until 
it crystallizes. The crystals are separated from the syrup and 
later they are dried in a machine called a granulator in which 
the crystals are separated from one another. By pressing the 
moist crystals in a mold the loaf sugar is made. The cubes 
are later dried. 



CHAPTER VIII 
BEFRIGERATION AND ITS USES 

I. THE REFRIGERATOR 

425. Use of the Refrigerator. — The refrigerator is probably 
found in as many modern houses as is the furnace. It is 
probably also true that the health and comfort of the family 
and economy of living depend upon the use of the refrigerator 
during the summer months in as large a measure as they do 
upon modern methods of heating — furnace, steam, or hot water 
heating — during the winter months. Owing to the difficulty 
of securing ice, the cellar must still be used in many rural 
districts as a substitute for the refrigerator, just as the stove 
is used in the place of the more modern and adequate heating 
devices. In most town and city houses, the refrigerator is now 
considered a necessity. 

426. Principle of the Refrigerator. — Most decay is the re- 
sult of the action of microorganisms upon vegetable or animal 
matter. Fermentation, or the action of microorganisms, is 
hastened by moderately high temperature and plenty of mois- 
ture (Arts. 320 to 328). Lowering the temperature of foods 
or lessening the moisture in the foods delays decay. The func- 
tion of the refrigerator is to ward off or delay decay as far as 
possible. It does this by providing a stream of cool, very dry 
air in which the foods are placed. The effectiveness of the re- 
frigerator depends largely upon the circulation of the air 
within it. The stronger the circulation, the more effective the 
refrigerator in preventing decay (see Chap. VI, Microorgan- 
isms). 

427. Construction of the Refrigerator. — The refrigerator 
is practically a box, the walls of which are usually made of 
several thicknesses, some of the materials being selected be- 
cause they are poor conductors of heat. Because air is a poor 
conductor of heat, most refrigerators are constructed with an 

358 



THE REFRIGERATOR 



359 



air space in the walls. This air space is usually packed some- 
what loosely with some substance such as charcoal or mineral 
Tvool or other poor conductors. This packing serves to break 
up convection currents which otherwise would be produced in 
this air space (Fig. 219). Air is a poor conductor of heat 
when not in motion, but, as we saw in the study of furnaces, 
it is a very effective agent in the transference of heat when it 
is moving in the form of convection currents. 

428. Styles of Refrigerators. — Refrigerators are either 

TOP-ICING REFRIGERATORS, Or SIDE-ICING REFRIGERATORS (Fig. 

220). In the top-icing refrigerator the cold, descending 
column of air may pass downward at the 
center of the refrigerator while the warmer, 
Lighter air passes upward at the two sides as 
shown in Fig. 220; or the cold, descending 
column may pass downward at one side of the 
refrigerator while the warmer, lighter air 
passes upward at the other side. In the side- 
icing refrigerator the air current is evidently 
always downward on the ice side and upward 
on the food side. The top-icing refrigerator 
usually affords a much larger ice capacity 
compared with the food capacity than does the side- 
icing refrigerator. On this account, when both ice boxes 
are filled, we should expect a somewhat lower tempera- 
ture in the top-icing than in the side-icing refrigerator. On 
the other hand, since in the side-icing refrigerator the food 
compartment extends the entire height of the refrigerator, the 
columns of cold air and of warm air are considerably higher 
than is possible in the top-icing refrigerator of the same ca- 
pacity. This insures very perfect circulation, which is an 
essential feature of a good refrigerator. 

429. Temperature Obtained and the Cause of Circula- 
tion. — In a good refrigerator well filled with ice, the tempera- 
ture of the air as it leaves the ice compartment and enters the 
food compartment is usually from 40° to 45°F. As the air 



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1 

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a. 


Fig. 2 19.— Walls 
of a refrigerator. 



360 



REFRIGERATION AND ITS USES 



leaves the food compartment and enters the ice compartment, 
its temperature is often raised to 55° or even 60°F. This 
difference in temperature is the cause of the circulation, the 
warmer, moist air being considerably lighter per cubic foot 
than the cooler, dry air (Arts. Ill and 115). 




Fig. 220. — Top-icing refrigerator and side-icing refrigerator. 

Table X. — Weight of 1 Cu. Ft. op Air Saturated with Water 

Vapor; Also, Weight op the Water Vapor in Each 

Cubic Foot op Air 



Tempera- 
ture, 


Weight of 

saturated 

air, 

grains 


Weight of 
water 
vapor, 
grains 


Tempera- 
ture, 
P.° 


Weight of 

saturated 

air, 

grains 


Weight of 
water 
vapor, 
grains 


—30 


650 


0.12 


40 


556 


2.85 


—20 


634 


0.21 


50 


544 


4.08 


—10 


620 


0.36 


60 


533 


5.75 





606 


0.56 


70 


521 


7.98 


+10 


593 


0.87 


80 


509 


10.93 


20 


580 


1.32 


90 


497 


14.79 


30 


568 


1.96 


+100 


487 


19.77 



The difference in weight of a cubic foot of air at the dif- 
ferent temperatures from — 30° to 100°F. is more clearly 
shown by the curve, Fig. 221. If the temperature of the air 



THE REFRIGERATOR 



361 



in a refrigerator varies from 40° on the ice side to 55 °F. on the 
food side, the weight of 1 cu. ft. of air will vary from 556 
grains to about 538 grains. This means that the warmer air 
is only about 2 %o as heavy as the cooler air. This difference 
in weight is sufficient to secure a convection current of con- 
siderable strength. 

Exercise 75.— A Study of the Temperature in a Refrigerator 
(a) Open the doors of a refrigerator and study carefully its 
construction. Is it top-icing or side-icing? If it is a top-icing 
refrigerator, determine whether the cold air drops out of the ice 
box at the center of the refrigerator or at one side. Also determine 
whether the warm air enters the ice compartment at one side only or 
at both sides. 



700 gr. 






























600 gr. 


























































*"»"• 


























































^ 400 gr. 

6 

C300gr. 



















































































































£ 200 gr. 


























































^100gr. 


























































Osr. 































0000 00 

N M H rt M 



s ssgiSb 



Fig. 221. 



Temperature 

-Curve showing density of air at different temperatures. 



(b) Having determined the course of the convection currents in 
the refrigerator, place the thermometer in this current close up to 
the opening through which the air passes as it leaves the ice com- 
partment and enters the food compartment. 1 Close all of the doors 
for about five minutes; then open one door and quickly read the 
thermometer without removing it from the air current. In like man- 
ner determine the temperature of the air as it leaves the food 
compartment and enters the ice compartment. 

If possible, repeat these experiments with a second refrigerator. 

1 It is well to wrap the bulb of the thermometer with asbestos cloth 
or paper to prevent the mercury from rising quickly when the ther- 
mometer is taken from the refrigerator. 



362 REFRIGERATION AND ITS USES 

The temperature obtained in this experiment will depend 
upon several things: (1) Construction of the refrigerator: (2) 
amount of ice in the ice compartment; (3) temperature of 
the room ; (4) amount and kind of food in the food compart- 
ment. Show how each of these factors affected # the tempera- 
ture in the refrigerator you examined. 

430. Meaning of Absolute Humidity, Saturation, Relative 
Humidity, and Dew Point. — In order to understand how the 
temperature of the air determines the amount of moisture 
which the air within a refrigerator contains, it is necessary 
that we learn some new terms and their exact uses. 

Definitions. — 

Absolute Humidity. — By absolute humidity we mean 
the weight of moisture or water vapor actually contained in 
one unit volume of air, usually expressed in grains per cu. ft. 

Saturation. — We speak of the air as being saturated or 
as having reached the point of saturation when it contains 
all the moisture, or water vapor, it can possibly contain at 
that temperature. 

In the table given above (Art. 429), the third column gives 
the absolute humidity of fully saturated air at the various 
temperatures given in the first column. For example, at 
0°F. the absolute humidity of saturated air is 0.56 grain 
per cu. ft, while at 70°F. it is 7.98 grains, or nearly fifteen 
times as great. 

Relative Humidity. — Relative humidity is the ratio of 
the absolute humidity of air at any temperature to the abso- 
lute humidity of air were it saturated at the same temperature. 

Suppose the air in a schoolroom is found to contain 4 grains 
of water vapor per cu. ft. when the temperature is 70°F. 
The relative humidity of the air is then expressed as the ratio 
of 4 grains to 7.98 grains, of 4,0 %.98, or very nearly y 2 . The 
relative humidity is usually expressed, however, not as a 
fraction, but as a per cent. In this case we say the relative 
humidity is 50 per cent. 

Dew Point. — Dew point is the temperature at which air 



THE REFRIGERATOR 



363 



containing a certain amount of moisture per cubic foot, that is, 
having a certain absolute humidity, becomes saturated, and 
dew forms. 

Suppose, as before, that the air in a schoolroom is at 70°F. 
and that it contains 4 grains of moisture per cu. ft. Now, 
if the temperature in that room were lowered, the air would 
become more nearly saturated, that is, its relative humidity 
would become higher, because the actual amount of moisture 
per cubic foot # would remain the same while the amount of 



20.0 gr. 

19.0 

18.0 

17.0 

16.0 

15.0 gr. 

14.0 

13.0 

12.0 

11.0 

10.0 gr. 

9.0 

8.0 

7.0 

6.0 

6.0 gr. 

4.0 

3.0 

2.0 

1.0 

0.0 gr. 



■ 



Temperature 



Fig. 222.— Curve showing weight of water vapor in saturated air at 
different temperatures. 



moisture it might contain would decrease with the fall in 
temperature. By examining the table above, or still better 
by examining the curve (Fig. 222), we see that the air will 
become saturated when the temperature has fallen a trifle 
below 50°, or about 49°F. Its relative humidity would then 
be 100 per cent. This temperature at which the air becomes 
completely saturated is called the dew point. If any object 
whose temperature is at, or below 49°F., is taken into this 
room, a portion of the moisture will be condensed upon this 
object, forming dew. This is exactly what takes place when 



364 REFRIGERATION AND ITS USES 

a pitcher or glass of cold water stands for a few minutes on a 
warm summer day. The pitcher or glass becomes covered 
with dew. Often dew stands in drops on a pitcher or glass 
containing ice water. 

431. Why the Air within the Refrigerator Is Dry. — In 
many portions of the United States the air on a summer day 
frequently reaches a temperature of 90 °F., while at the same 
time the relative humidity is often as high as 80 or 85 per 
cent. We see, by reference to Table X, Art. 429, or to the 
curve (Fig. 222, B), that this means that the air contains 12 
cr 12.5 grains of moisture per cu. ft. At the same time, 
the air within the refrigerator is still more nearly saturated. 
But, since the temperature of that air is not higher than 
50° or 55 °F., the largest amount of moisture it can possibly 
contain is only about 4 or 4.5 grains per cu ft., or about one- 
third of that contained by the air outside. Again, as the air 
circulates through the ice compartment, much of it actually 
comes directly in contact with the ice. This must mean 
that the air for the moment is cooled nearly to 32°F., the 
temperature of the ice. All of the moisture in this air in 
excess of about 2 or 2.5 grains per cu. ft., therefore, is de-> 
posited in the form of dew upon the ice. Show this to be 
true by reference to the curve (Fig. 222, C). It is there- 
fore evident that the air, as it flows from the ice compartment 
into the food compartment, does not contain more than about 
one-fifth, or at most one-fourth, as much moisture as the air 
in the room. The air, then, as it flows from the ice compart- 
ment into the food compartment, is cold and contains but 
little moisture, notwithstanding the fact that it is saturated. 

432. Effect of the Dry Air within the Refrigerator upon 
Foods. — "When this stream of cold, dry air leaves the ice 
compartment and enters the food compartment, it takes up 
heat from all the contents of the food compartment. As this 
air rises in temperature, its capacity for holding moisture 
increases rapidly, that is, its relative humidity is lessened; 
it is not longer saturated. Since most of the provisions usu- 



THE REFRIGERATOR 365 

ally placed in the refrigerator contain considerable moisture, 
evaporation takes place and the foods become drier. It is 
for this reason that fruits, such as apples, oranges and lemons, 
as well as other kinds of provisions, often dry up and wither 
instead of suffering ordinary decay when placed in a good 
refrigerator. Common table salt often absorbs so much mois- 
ture in the summer that it can not be shaken from a salt 
shaker. This can be prevented by placing the shaker in the 
dry air of the refrigerator. 

433. How the Refrigerator Aids in Preserving Food. — 
"We have seen in Chap. VI that the greatest competitors for 
food that man has are microorganisms, molds, yeasts and bac- 
teria. All foods which man wishes to keep in store for any 
considerable length of time must be protected from micro- 
organisms. We can protect our foods by adopting one or more 
of several methods. First, we may so dry our foods that they 
do not contain sufficient moisture to support microorganisms ; 
second, we may preserve the food stuffs by heating them to 
such a temperature that all microorganisms and their spores 
are killed, then sealing the food in cans which prevent other 
microorganisms from getting into them (canning of foods). 
Food stuffs thus prepared may be kept almost any length of 
time. 

In actual practice, however, we wish to keep some foods 
for a shorter time without either canning them or drying 
them. Nearly every family has a supply of food left over 
after every meal which should be saved for the next meal. 
Milk and fresh meats are generally kept in stock for a day 
or so in advance of use. By placing such food stuffs in a re- 
frigerator where the air is quite dry and the temperature is 
rather low the action of microorganisms is so retarded that the 
foods remain almost unaffected by microorganisms for some 
time. The length of time which foods may thus be preserved 
depends upon the nature of the food, the temperature main- 
tained within the refrigerator, the dryness of the air within 
the refrigerator and the circulation of air within the refriger- 



566 REFRIGERATION AND ITS USES 

ator. The ordinary refrigerator in the home usually serves to 
preserve food from the attack of microorganisms for a few 
days only, but by the modern methods of cold storage (Arts. 
323 and 447) foods are regularly kept for long periods of time, 
from season to the next season. 

434. What Keeps the Refrigerator Cool. — It is not possible 
to construct a refrigerator of such material and in such a 
manner as entirely to prevent heat from getting into it, even 
when all doors are closed. If this were possible, very little 
ice would be needed to operate it. Since heat is certain to 
penetrate the refrigerator from every side, and at all times, 
this heat must be taken up or absorbed by the ice. In Art. 
127, we learned that heat used in melting ice is called heat 
op fusion. The cooling of the refrigerator is due almost 
entirely to the absorption by the ice of this heat of fusion; 
that is, the heat is consumed simply in melting the ice. 
Occasionally we hear of someone's wrapping the ice in paper, 
to prevent melting, before placing it in the refrigerator. 
This, of course, is an error. Just to the extent that wrapping 
actually prevents melting as intended, the presence of the ice 
in the refrigerator is useless. Nevertheless, good judgment 
on the part of the operator may lessen considerably the 
amount of ice required to operate the refrigerator. The re- 
frigerator should be placed in the dryest and coolest place 
possible, consistent with convenience. 

435. Rear-icing and Built-in Refrigerators. — Most manu- 
facturers, when requested, now furnish refrigerators with a 
door to the ice compartment on the back, or rear, of the re- 
frigerator. This device is often of great service, inasmuch 
as it enables the ice man to fill the refrigerator without com- 
ing inside the house. The refrigerator is placed with its back 
against the outside wall. An opening is made in the wall 
corresponding to the rear door of the refrigerator. This 
opening is fitted with a door also. This opening is generally 
reached from a porch; therefore, the refrigerator can be as 
easily filled from the outside as it could be from the inside 



THE REFRIGERATOR 



367 



of the house, thereby saving much dirt and inconvenience. 
In many modern houses the refrigerator is ''built-in," that 





Fig. 



-A built-in refrigerator. 



is, it is constructed as a part of the house just as truly as 
is the staircase (Fig. 223). 

436. The Refrigerating Machine for Home Use. — During 
recent years many devices have been 
constructed to take the place of the re- 
frigerator in the home. They all in- 
volve the principles employed in the 
manufacture of ice and in cold storage 
plants (see next two sections). Fig- 
ure 224 shows one such device. It is 
really a small cold storage plant at- 
tached to an ordinary refrigerator. 
On top of the refrigerator is a com- 
gas. (Dry ammonia gas, also carbon 
pressor for compressing sulphur dioxid 
dioxid are sometimes used instead.) 
The compressor is run by a small elec- 
tric motor. The compressed gas passes through cooling coils 
where it is liquefied. It then passes into the refrigerating 




Fig. 224.— A mechanical 
refrigerator. 



368 REFRIGERATION AND ITS USES 

coils which are in the ice compartment of the refrigerator. 
Here the liquid sulphur dioxid is released from pressure and 
changes into a gas, producing a lower temperature and dryer 
air than can be secured by the use of ice. (See II, of this 
chapter). 

. 437. Care of the Refrigerator. — We have seen that the pur- 
pose of the refrigerator is to delay or ward off the action of 
microorganisms upon food stuffs. It is not sufficient that the 
temperature of the air within the refrigerator and the food 
be kept at as low a temperature as is possible. In addition 
to this the interior of the refrigerator must be kept just as 
clean as possible. 

Freshly cooked foods, or fresh fruits and vegetables, are not 
well seeded with microorganisms or the spores of microorgan- 
isms, although they are certain to contain some such organisms 
and spores. If the conditions within the refrigerator are un- 
favorable for the rapid growth and multiplying of such or- 
ganisms, the multiplication will be slow. If, on the other 
hand, the interior of the refrigerator is dirty, if old food stuffs 
are allowed to remain scattered about within the refrigerator, 
or if more or less liquid foods have been spilled within the 
refrigerator and not thoroughly removed, or if the drain pipe 
is allowed to go unclean ed, — any one or all of these condi- 
tions afford excellent culture beds for all kinds of molds, 
yeasts and bacteria. In refrigerators not properly cleaned 
the air is filled with the spores from these microorganisms. 
These spores settle upon the foods and molding, fermentation 
and decay takes place rapidly. 

Every refrigerator should frequently be thoroughly cleaned 
and rinsed with hot water, a's near boiling hot as possible. 
The drain pipe should not be omitted. 

II. MANUFACTURED ICE AND FREEZING MIXTURES 

438. Need of Manufactured or Artificial Ice. — Without 
manufactured ice it would be impossible to make use of the 
refrigerator in many portions of the civilized world. Even 



MANUFACTURED ICE AND FREEZING MIXTURES 369 

in climates where natural ice is produced in sufficient quan- 
tities, artificial ice is regarded as a necessity for many pur- 
poses on account of its greater purity. Most towns and cities 
of any considerable size have their ice factories. Artificial 
ice is today in such common use that we should learn some- 
thing about the principles involved in its manufacture. 

439. The Ice Plant. — The essential parts of the ordinary 
plant for the manufacture of ice are: (1) Steam boilers and 
a steam engine; (2) an ammonia compressor (B, Fig. 225) ; 




Fig. 225. — Diagram of an ice factory. 

(3) cooling coils, through which the ammonia passes and over 
which flows constantly a stream of cool water (C, Fig. 225) ; 

(4) a tank of brine through which the ammonia pipes run 
(Fig. 225) ; (5) cans containing purified water which is to be 
frozen (G, Fig. 225). There are usually also mechanical de- 
vices for handling the blocks of ice, and frequently additional 
boilers for the distilling of the water which is to be frozen. 

Before we can understand the use of these parts of the plant 
and the process followed, we need to know some of the speciaL 
properties of ammonia. 



370 REFRIGERATION AND ITS USES 

440. Some of the Properties of Ammonia. — When study- 
ing evaporation (Art. 12, Ex. 10, we learned that when any 
liquid evaporates much heat is absorbed, or, as we commonly 
say, cold is produced. This last way of speaking is really not 
incorrect if we fully realize that cold is simply absence of heat ; 
it is better, however, to speak of the heat's being absorbed. 
We should also recognize that it is the heat of vaporization 
(Art. 127) which is absorbed. We also saw that those liquids 
which evaporate most rapidly absorb heat most rapidly ; they 
feel the coldest on the back of the hand. The substances 
studied were water, alcohol and gasoline. But each of these 
substances is a liquid at ordinary temperatures, and each 
of them boils under the pressure of the atmosphere at a tem- 
perature higher than that of the air about us. (Recall the 
boiling temperature of each of these substances.) Evidently, 
then, each of these three substances will change from the 
liquid form to vapor form rapidly, that is, it boils only when 
raised to a rather high temperature. Further, it is only 
when a liquid is boiling that it absorbs the heat of vaporiza- 
tion most rapidly. 

We see now that if we can obtain some substance in the 
liquid form which evaporates very rapidly, or even boils, at a 
temperature below the freezing point of water, we can then 
allow this liquid to evaporate and absorb heat, taking it from 
water till the water freezes. This is exactly the principle em- 
played in the manufacture of ice, and ammonia is the liquid 
most commonly used. 

Nearly everyone is somewhat familiar with ammonia. It 
is the gas that escapes from common aqua ammonia, or spirits 
of hartshorn, which may be purchased at any drug store. 
This common aqua ammonia is simply water which has ab- 
sorbed large quantities of ammonia. When aqua ammonia is 
exposed to the air, the ammonia escapes. Its stinging, biting 
odor is familiar to all and is easily recognized. The ammonia 
with which we commonly come in contact, then, is always in 
the gaseous form. This same ammonia, however, can be 



MANUFACTUKED ICE AND FREEZING MIXTURES 371 

changed into liquid form by compressing it. The pressure re- 
quired to change ammonia gas into liquid form depends upon 
its temperature ; the higher the temperature, the greater is the 
pressure required. For any given temperature, there is a 
corresponding pressure which is just sufficient to liquefy the 
gas. This relation of temperature to pressure is often stated 
in another way: We often speak of the boiling points cor- 
responding to a given pressure. It must be clearly under- 
stood, however, that the boiling point corresponding to a 
given pressure is exactly the same temperature as the lique- 
fying point corresponding to that pressure. Recall that water 
boils and steam condenses at the same temperature. 

Table XI. — Pressuee and Corresponding Boiling Point 
of Ammonia. 

Pressure At™™^™.™ Boiling point 

lb. per sq. in. Atmospheres or liquef ££ g point 

15 lb 1 atmosphere — 29°F. 

30 lb 2 atmospheres 0°F. 

34 lb 2.3 atmospheres 5°F. 

63 lb 4*.2 atmospheres 32°F. 

107 1b 7.1 atmospheres 60°F. 

130 lb 8.6 atmospheres 70°F. 

155 lb 10.3 atmospheres 80°F. 

From this table we see that to change ammonia from a gas 
to a liquid at the ordinary temperature of 70 °F. requires a 
pressure of about 130 lb. per sq. in. We also see that at the 
pressure of 1 atmosphere, or 15 lb. per sq. in., the ammonia 
will be in the liquid form if the temperature is below — 29 °F 
and in the gaseous form if the temperature be above — 29 °F. 
(Fig. 227). 

Note: It is important that w.e remember that the ammonia 
used in refrigerating plants is the pure, dry ammonia; never 
the water solution of ammonia, or aqua ammonia. 

441. How the Water is Frozen. — The ammonia to be used 
in the plant is received from the manufacturing chemist in 
strong metal containers. It is highly compressed, and, there- 



372 



REFRIGERATION AND ITS USES 



fore, is in the liquid form. This ammonia is fed into the 
system through the opening, A, Fig. 225. As the ammonia 
escapes from the high pressure, it boils violently and changes 
to the gaseous form. As the compressor is running, the 
ammonia is drawn directly through the lower valve into the 
cylinder of the compressor, B, Fig. 225. The piston then 
forces it through the upper valve into the pipe leading to the 
cooling coils, C. As the ammonia is compressed, it becomes 
very much heated, and, although the gas is subjected to a 



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Fig. 226. — Curve showing the properties of ammonia. 

pressure of 140 lb. or more per sq. in., it still retains its 
gaseous form. The cooling coils, C, are kept cool, however, by 
being constantly drenched with cool water. As the heated am- 
monia gas passes through these coils, it is cooled. Referring 
again to the table given in the last article, we see that the 
ammonia will liquefy under a pressure of 140 lb. as soon as 
the temperature drops to about 75 °F. Now the cooling coils 
can be kept at a temperature as low as 75 °F. by drenching 
them with water from the city mains or pumped from wells. 



MANUFACTURED ICE AND FREEZING MIXTURES 373 

It should be carefully noted that the cool water carries away 
two distinctly different portions of heat from the ammonia. 
First, the highly heated ammonia gas is cooled down to the 
temperature of the water, that is, the water carries away the 
sensible heat (Art. 126) . Second, when the ammonia changes 
from the gaseous form to the liquid form, it gives up exactly 
as much heat as it absorbs when it changes from the liquid 
form to the gaseous form. The heat given off when a gas 
liquefies is called heat of condensation. This heat of con- 
densation exactly equals the heat of evaporation. (Art. 127.) 

The liquid ammonia accumulates in the reservoir (D, Fig. 
225). It is now at about 70°F. and under about 140 lb. of 
pressure. "When the liquid ammonia has accumulated in the 
reservoir to the desired amount, as shown by the glass gauge, 
the valve A is closed and no more ammonia is fed into the 
system.. The valve, E, is now opened and the ammonia is 
permitted to flow into the coil of pipes submerged in the 
brine. Being released from pressure, as soon as it escapes 
through the valve, E, the ammonia begins to evaporate rapidly, 
even boil. This means that it takes up heat of vaporization. 
It receives this heat from the brine. The brine consequently 
drops in temperature. When cans of pure water are placed 
in this brine, as G, Fig. 225, the brine absorbs heat from the 
water and continues to do so till the water is frozen. As 
long as the compressor is kept running, the circulation of 
the ammonia continues. 

442. Why Brine is Used and How the Temperature of the 
Brine is Regulated. — "When studying the thermometer, we 
saw that Fahrenheit got the temperature which he called zero 
on his thermometer by mixing salt and crushed ice (Art. 17). 
Now if just enough salt is mixed with ice to make a saturated 
solution 1 when the ice melts, the melting point of the mix- 
ture is a little lower than the lowest temperature Fahrenheit 

iNote: A saturated solution of salt is one in which no more salt 
will dissolve in the water. At ordinary temperatures 2% lb. of water 
will dissolve about 1 lb. of salt. 



374 REFRIGERATION AND ITS USES 

obtained. It is about — 7°F. But it should be carefully 
noted that the melting point of such a mixture is also the 
freezing point of a saturated solution of salt and water, just 
as the melting point of pure ice is exactly the freezing point 
of pure water (Art. 16). The saturated solution of salt and 
water, then, can be frozen only by lowering the temperature 
to about — 7°F., which is 39° below the freezing point of 
water. 

In operating an ice plant it is customary to cool the brine 
to about 16° or 18 °F. The temperature of the brine can 
easily be governed by opening wider or partly closing the 
regulating valve. It will be noticed that the compressor 
not only compresses the ammonia gas on the compression 
side of the regulating valve E, i.e., in the cooling coils, but 
that at the same time it is reducing the pressure on the 
other side of the valve, i.e., in the pipes in the brine vat. 
It also becomes evident that if the regulating valve is nearly 
closed the pressure becomes great on the compression side 
while it is reduced on the exhaust side. On the other hand, 
opening the valve wider permits the pressure to become some- 
what nearer equal on the two sides. Hence we speak of the 
high side and the low side of the plant. The high side 
comprises that portion of the ammonia pipes from the com- 
pressor to the valve, E. The low side comprises the portion 
from the valve E, to the compressor. Referring to the table 
(Art. 440), we see that at a pressure of 34 lb. the boiling 
point of ammonia is 5°F. In operating the ice plant, the reg- 
ulating valve is usually so set that the pressure on the low 
side of the valve, i.e., in the pipes in the brine vat, is main- 
tained at about 34 lb. Since the temperature of the brine is 
usually from 10° to 15° above the temperature of the pipes, 
the temperature of the brine is about 16° or 18 °F. 

443. Purity and Cost of Manufactured Ice. — Practically all 
impurities of every kind are removed from the water by dis- 
tilling it before it is placed in the cans to be frozen. Even 
though air be the only impurity present when freezing takes 



MANUFACTURED ICE AND FREEZING MIXTURES 375 

place, the ice will be filled with small bubbles and therefore 
will be clouded and opaque. It is the presence of a very 
small amount of air which the water reabsorbs before freezing 
can take place, which gives the center of the ice cake the 
whitish, opaque appearance familiar to all users of artificial 
ice. Even small quantities of dissolved solids generally give 
the ice a yellowish or brownish tinge. When frozen in cans 
by the method here described, only pure water can give clean, 
colorless ice; therefore, only distilled water is used. As far 
as possible the exhaust from the engine which runs the com- 
pressor is used. Since this does not furnish sufficient water, 
generally, steam from the extra boiler mentioned above (Art. 
439) is also condensed and used. 

In the southern portion of the United States and in many 
northern portions which are remote from bodies of fresh 
water, manufactured ice can be produced at less expense than 
natural ice can be obtained. The average cost of producing 
artificial ice is now generally about $2 per ton. The cost to 
the consumer is, however, much more than this, owing to the 
expense of handling and the large loss due to melting which 
necessarily accompanies its distribution during warm weather. 

444. Freezing of Ice Cream. — The freezing of ice cream 
involves some of the principles just described. Finely broken 
or crushed ice is mixed with common salt and the mixture is 
then packed in the freezer, around the can containing the 
cream to be frozen. As we saw in Art. 16, such a mixture 
of ice and salt has a melting point far below the melting 
point of pure ice. Or, we may express the same truth in 
another way. We may say that the freezing point of a 
saturated solution of salt and water is — 7°F., or 39° below 
the freezing point of pure water (Art. 16). If a mixture 
of one-third salt and two-thirds crushed ice is used in the 
freezer, the temperature of the mixture will tend to fall to 
this point as the ice melts. 

It is evident that as the first portions of the ice melt, the 
^ater formed will dissolve some of the salt, forming a satu- 



376 



REFRIGERATION AND ITS USES 



rated solution of salt water. We also know that as the ice 
continues to melt it absorbs large quantities of heat. Most of 
the heat absorbed by the ice, when melting, must be taken 
from the freezer and from the can of cream. Both will, 
therefore, fall in temperature. Since the cream freezes at a 
temperature much higher than the freezing point of the 
mixture, it is evident that if a sufficient quantity of salt and 
ice is used the cream can be completely frozen (Fig. 227). 

The only puzzling question in the process of freezing cream 
is this: Why does the ice continue to melt when the tern- 




i 



Fig. 227. — An ice cream freezer. 



perature falls below 32°F., the ordinary melting point of ice? 
The answer is: A mixture of salt and ice can exist as salt 
and ice only at a temperature of — 7°F., or lower. If salt is 
placed upon ice at a higher temperature, the ice melts and the 
salt dissolves in the ice water. If there is enough salt, a 
saturated solution of salt is formed. Now a saturated solu- 
tion of salt will not freeze at a temperature above — 7° F. 
In the ice cream freezer we have a mixture of the three sub- 
stances, salt, ice, and a nearly saturated solution of salt. 
As long as the supply of salt and ice holds out, the ice con- 
tinues to melt and absorb heat; the temperature of the 



COLD STORAGE 377 

mixture, therefore, tends to fall toward the freezing point of 
the salt solution, — 7°F. 

III. COLD STORAGE 

445. Effect of Cold Storage on Modern Life. — The develop- 
ment of plants for the production of cold by artificial means 
has not only given us ice in greater abundance and in greater 
purity, but it has also made possible the construction of 
many enormous cold storage plants. In these cold storage 
plants, the surplus of perishable produce, such as eggs, butter, 
poultry, beef, fruits, and vegetables is stored during the 
seasons of abundance. In cold storage this perishable 
produce is preserved for weeks, or even months, much of it 
suffering but little deterioration. Before the establishment 
of cold storage plants, the markets were often flooded with 
certain fruits for a short period ; in a few weeks, however, the 
entire year's supply of these fruits was either consumed or 
had decayed and was lost. Similarly, the production of eggs 
is much greater during the spring and early summer than 
at other seasons of the year. Formerly the supply of eggs 
during the spring was so greatly in excess of the demand that 
the price fell to a ridiculously low mark, and many eggs even 
went to waste. During the winter months, on the other hand, 
eggs were often practically unobtainable at any price. Since 
the advent of cold storage, however, many kinds of fruit, eggs, 
and other kinds of perishable produce, are obtainable at any 
season of the year and at prices which vary but little from 
season to season. In this and other ways, cold storage has 
greatly modified modern life. 

446. Construction of a Cold Storage Plant. — A modern 
cold storage plant so closely resembles an ice plant that no 
extensive explanation is necessary. The plant consists of a 
compressor, A, operated by a steam engine, B (Fig. 228). 
The ammonia is cooled and liquefied in the cooling coils, C. 
It then collects in the reservoir, D, and finally is permitted to 
pass through the regulating valve, E. The "high side," then, 



378 



REFRIGERATION AND ITS USES 




COLD STORAGE 379 

is exactly like the "high side" of a manufactured ice plant. 
After passing through the valve, E, the ammonia vaporizes 
in the pipes submerged in the brine in the vat, F. After 
vaporizing, the ammonia returns to the compressor through 
the pipe, c-c. Thus we see that the "low side" is also the 
same as in the case of the ice plant. The brine vat, however, 
is not usually within the storage room at all. The chilled 
brine is forced by the pump, G, through the pipe, d-d, to 
the absorbing coils, H and H, in the storage rooms. After 
passing through these coils, the brine returns to the vat, F. 

447. Temperature Required for Cold Storage and How 
Controlled. — Different kinds of produce keep best when 
stored at different temperatures. Some fruits are usually 
stored at about 36°F.; others at about 32°F. ; fresh meat at 
about 25°F. ; poultry at about 15°F.; and fish at about 0°F. 
To obtain a given temperature in the storage room it is 
necessary that the boiling point of ammonia be controlled. 

The coils submerged in the brine vat are evidently cooled 
about to the boiling point of the ammonia. But it is generally 
the case that the brine is about 10° higher than this. More- 
over, the brine is generally about 6° warmer when it returns 
from the coils, H-H, than when it passes through the pump 
on its way to the coils. Again, the air in the storage room is 
usually about 6° warmer than the brine within the coils, H-H. 
Altogether, then, the air in the storage room is about 22° 
above the boiling point of ammonia. 

Now we have already seen how the boiling point of the 
ammonia is controlled by controlling the pressure on the low 
side of the refrigerating system. In the storing of fruits 
where the temperature should be 36°F., the boiling point of 
the ammonia must be about 22° lower, or about 14° F. By 
referring to Fig. 225, we see that the boiling point of ammonia 
is 14°F. when under a pressure of about 44 lb. to the sq. in. 
Therefore, in storing such fruits, the regulating valve is so 
set as to maintain a pressure of about 44 lb. on the low side. 

Most kinds of fruit keep best when stored slightly above 



380 REFRIGERATION AND ITS USES 

32 °F. If it is found that the temperature of the air in the 
store room is 22° above the boiling point of the ammonia, we 
see that the boiling point of the ammonia would need to be 
kept at about 10°F. Referring to the curve we find that the 
pressure of the low side should be about 40 lb. 

In a similar manner, show that the pressure on the low side must 
be about 33 lb. for the storing of meat which keeps best at about 
25 °F.; at about 27 lb. for the storing of poultry at 15 °F.; and that 
the pressure on the low side must be about 18 lb. for the storing of 
fish which must be kept at zero F., if the air in the store room is 
22° above the boiling point of the ammonia in the low side pipes. 

448. Refrigeration and Transportation. — A fruit has a life 
history extending from the formation of the fruit bud to the 
decay of the ripened fruit. Some fruits have short life his- 
tories, others, longer. Fresh fruits, when not overripe, are 
alive ; they do not readily decay. Some fruits, such as straw- 
berries, die very soon after reaching maturity ; others, such as 
winter apples, remain alive for many weeks after being re- 
moved from the tree. The purpose of cold storage of fruits 
is to delay the ripening process so that the life of the matured 
fruit may be extended over as long a period as possible, in 
some cases even till the next year 's crop matures. In the case 
of short-lived fruits it is necessary to get them into the hands 
of the consumer* as quickly as possible. But the majority of 
the consumers live in the larger cities, like New York, Phila- 
delphia, Boston, and* Chicago, long distances from the more 
productive fruit growing sections. 

It was formerly practically impossible to transport short- 
lived fruits from the field to the consumer. Today, however, 
by using modern refrigerator cars, oranges are shipped from 
California to New York; strawberries from Mississippi to 
Chicago; peaches from Florida, Georgia, and Texas to the 
Boston market with little or no deterioration. Similarly, 
the markets of the world are supplied with fresh meat and 
poultry, killed and dressed in the slaughter houses of Kansas 
City and Chicago. 



CHAPTER IX 
GROUND-WATER AND GROUND-AIR 

I. GROUND-WATER 

449. What Becomes of the Rainfall? — We have seen that 
the annual rainfall in the United States varies from a few 
inches to 70 inches or more. The annual run-off, that is, the 
water which actually runs off the land through the streams, 
amounts to ahout % of the rainfall, or in different parts of 
the United States it varies from nothing to about 20 inches. 
What becomes of the rest of the rainfall? It sinks into the 
soil and becomes soil water which is the subject of our pres- 
ent study (Fig. 229). 

450. Visible and Invisible Water Supply. — The water in 
streams, lakes and oceans constitutes our visible water sup- 
ply. The water which sinks into the earth and disappears 
from view constitutes our invisible water supply. We all 
realize the value of our visible supply. From the earliest 
times man has used water courses for highways ; he has used 
oceans and seas to carry himself and his goods from continent 
to continent ; he has used the streams and inland lakes to ex- 
plore the interior of continents and to trade with the native 
inhabitants. Many times the rapidly flowing stream has 
turned his mill and done work for him. The visible water 
supply has furnished him with water to drink and with water 
to irrigate his growing crops. In olden times all great civili- 
zations were located on or near the banks of bodies of water. 
Today we are less dependent upon the visible supply and 
many people live far away from oceans, streams and lakes. 
Many of their wants are met by using the invisible water 
supply. 

451. Uses of the Invisible Water Supply. — Nearly all 
plant life depends upon the invisible water supply for the 

381 



382 



GROUND-WATER AND GROUND-AIR 



water they must have. "Without plant life animal life would 
quickly perish from the earth. Again, man must have a sup- 
ply of water for drinking and cleansing purposes. Probably 
a majority of mankind in civilized countries obtain this sup- 
ply of water from the earth's invisible supply. 

452. The Source of Well Water. — While it is true that 
upon the frontier of civilization men still get their water sup- 
ply from streams, and while it is true that most large cities 
consume so large an amount of water that they, too, are 




Fig. 229. — Mean annual run-off, United States. 

obliged to take their supply from streams or lakes, still it is 
probable that in the United States a larger number of people 
are using drinking water from wells. Since wells are such a 
common source of water supply, we may well ask, Where does 
the water come from which we pump from our wells f 

There is no mystery as to where the water comes from in 
certain seasons of the year. When heavy rains have been 
frequent and the ground is soaked full of water, it is easy to 
see that wells, which often are merely holes in the ground, will 



GROUND-WATER 383 

also be filled. But where does the water come from which 
fills our wells partly full even after mouths of hot, dry 
weather? There are weeks, eveu mouths, at a time, iu some 
sections, when but little rain falls and this merely wets the 
surface of the soil, which is soon dried by evaporation. Evi- 
dently the ground must in some way serve as a great reservoir 
storing a supply of water which we are able to draw upon as 
needed. That this must be so is made more evident by the fact 
that a good, ''never failing" well pumped empty at a certain 
time is found soon to contain as much water as it did before 
the pumping took place. 

453. The Earth a Great Sponge. — The fact is that the earth 
is not unlike a great sponge. We have all seen a pail of water 
quickly disappear when poured upon the dry earth. We have 
all seen several inches of rain fall within a few hours, and 
still much of it disappeared nearly as fast as it fell if the 
earth was very dry when it began to rain. Over most of 
the earth's surface, the earth's crust is composed chiefly of 
porous soil. This porous soil holds water much as a sponge 
does. 

454. Ground-water. — The earth's crust is not composed of 
the same material at all depths as that at its surface. 
Through the upper Mississippi valley, for instance, we often 
find 2 or 3 ft. of black soil at the surface. Beneath this there 
may lie 6 or 8 ft. of yellow clay. Then, perhaps, is found a 
2- or 3-ft. vein of sand and gravel. Next, possibly, lies 10 ft. 
of blue clay. This may rest upon a foot of gravel. Beneath 
this gravel may lie a thick bed of less porous clay called 
hardpan. And so on down through bedrock we find layer 
upon layer of different substances. Each layer differs from 
the one above it not only in material of which it is com- 
posed, but also, and more important for our present purpose, 
in the ease with which water can pass through it, or its 

POROSITY. 

No matter how many different layers, or strata, of material 
there may be, or of what material those layers may be com- 



384 GROUND-WATER AND GROUND-AIR 

posed, in time, water finds its way down through into bedrock. 
Throughout the millions of years which have passed since 
the beginning of this earth, the water which has been falling 
in the form of rain has been soaking down through these 
layers of soil till the earth's crust in most places is quite satu- 
rated. This water is called the ground-water. 

Over much of the earth's surface, then, the rainfall has 
been, and is, sufficient nearly to saturate the soil with water. 
This does not mean that the ground is completely filled with 
water from bed rock quite to the surface all the year around. 
But it does mean that the ground-water has sunk deeper 
into the earth than man has as yet been able to penetrate, and 
that over much of the earth's area it comes nearly to the 
surface of the soil. When rains are frequent and heavy, the 
ground may be completely saturated near the surface. Dur- 
ing most of the months of the year, however, the spaces between 
the soil particles are not filled with water for some distance 
from the surface downward. If we penetrate the ground 
deeply enough, however, we come to a place where there is so 
much water in the soil that it fills the spaces between soil par- 
ticles completely. This leads us to the point where we must 
state definitely the meaning of a new term, water plane, or 

WATER TABLE. 

455. The Water Table, or Water Plane.— "While all of the 
soil is more or less moist, the moisture in the upper portions of 
the soil usually is not free, unabsorbed water. It is water 
which adheres closely to the soil particles and cannot be re- 
moved by ordinary means. Of this moisture, film water, 
we shall learn more, later. At present we are interested in 
the portion of ground-water which is undbsor~bed. This 
water does not adhere as moisture to the soil particles, but 
lies as free, unabsorbed water between the soil particles. It 
is the surface of this free, unabsorbed ground-water which is 
called the water table, or water plane. 

456. Relation of the Water Table to the General Surface 
of the Land. — It has been determined by experiment that the 



GROUND-WATER 



385 



water table follows, in the main, the general surface of the 
land. The water in any shallow well stands at exactly the 
height of the water table if no water be used from the well. 
The water in the well varies in height just as the water table 
varies. Numerous wells have been sunk on the rolling ground 
lying beside a lake. The well at the lake's shore has water 
standing in it at the lake's level. A well farther up the hill 
is found to have water standing in it at a level somewhat 
higher. The next well, still farther up the hill, has water 
standing at a still higher level. In almost every case the level 
at which the water stands in the various wells scattered over a 
considerable area of land bordering upon a lake, indicates 















































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g^jljjMjpBJfflMi 


























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jlllf^ 

















Fig. 230. — Relation of water table to the land surface. 

that the water table tends to follow more or less closely the 
general level of the land. "Where the land rises the highest; 
there the water table shows the same tendency to stand high 
in the soil (Fig. 230). 

457. The Explanation. — It is easy to see why the water 
stands higher in the soil back from a river or lake. We must 
remember that the rain falls equally on the earth's surface 
near the river or lake. Much of the rainfall soaks into the 
soil. It then soaks slowly down through the soil to the water 
table. When the water table gets higher than the surface of 
the river or lake, it tends to move horizontally into the river 
or lake. But it has to find its way through the soil, between 
the soil particles. The soil particles constantly block its pas- 
sage just as rocks block the free passage of water in the bed of 



386 



GROUND- WATER AND GROUND-AIR 



a shallow stream. The ground water, therefore, moves much 
more slowly down hill through the soil than it does down the 
more open bed of the river. The water level in the lake or 
river is, therefore, constantly at a lower level than the sur- 
face of the ground water in the soil near its banks. The 
farther back we go from the lake or river, the higher the level 
of the ground water stands. 

458. Drainage through the Soil. — Since a river's channel is 
usually considerably lower than the soil on either side, and 
also lower than the water table, we see that not only does the 
surface water flow into the river but that the soil-water is 



G*4z^z?y 




Fig. 231. — Ground-water and river-water. 



also constantly flowing through the soil into the river. This 
horizontal movement of soil-water, or lateral percolation, 
is usually very slow but varies with the nature of the soil 
through which it flows. Different tests show the rate of move- 
ment of this soil-water to vary from 5 feet to 100 feet per day. 

Roughly speaking, about % of the rainfall in the United 
States is carried off by the streams. Fig. 229 shows the 
amount of this annual run-off in the various sections of the 
country. Compare this map with Fig. 174, the annual rain- 
fall map. The remaining % of the rainfall evaporates from 
rivers, lakes, from vegetation and from the soil itself. 

459. Relation of the Ground-water to the River-water. — 



GROUND-WATER 387 

It is interesting and important to note the relation of the 
ground-water near a river to the water in the river bed. 
Anyone who has followed the course of a river far is aware 
that, in most cases, springs are common along its banks. In 
many cases where no running water flows down the banks, the 
banks are very moist, showing the near presence of free 
ground-water. The cause of springs is easily seen when we 
know that the conditions shown in Fig. 231 are not uncommon. 
On the river bank to the left we have the ideal conditions for 

a SPRING. 

Swimmers are aware of the fact that springs of cold water 
are often located in the very bottom of river beds. The 
colder ground-water rises into the river at many points. 
Figure 231 also shows how this may be so. 

Many cities, in attempting to secure an adequate Water 
supply, have constructed what are known as infiltration- 
galleries (Fig. 231). These are merely wells sunk beside 
the rivers. Sometimes from the bottom of the wells long 
horizontal galleries extend along beside the river or out be- 
neath it. Each gallery is, of course, bricked up to prevent 
the ground from caving into it. Other cities have buried 
filter-cribs in the bottom of the stream itself. In many 
cases it was expected that the river-water would find its way 
into the galleries and cribs. Such has rarely been the case. 
Repeated and frequent examinations of the water in such cases 
by chemists have nearly always shown that the gallery or the 
crib contains ground-water, not river-water. It is evident that 
the gallery or the crib has intercepted the ground-water on its 
way into the river. The general movement, then, of the 
ground^ivater along a river bed is nearly always into the 
river from either side and up into it from beneath. What 
forces the water up into the river from beneath? 

In some arid regions the flow of water along a river valley 
is the reverse of that just described. For example, along the 
Platte River in Colorado and western Nebraska the percola- 
tion of water is generally from the river off to either side into 



388 GROUND-WATER AND GROUND-AIR 

the soil. The river is fed by the melting of the mountain 
snows and, as the water runs out on the arid plains, its sur- 
face is higher than the general level of the water-plane. The 
water of the river, therefore, soaks out into the soil and in the 
dry season completely disappears. In the spring or early 
summer the river is said ' ' to come down ' ' from the mountains. 
Explain what is meant. 

II. GROUND-AIR 

460. Importance of Ground-air. — Closely related to ground- 
water and, more or less controlling its movements, is the 
ground-air. The upper portion of soil, down to the water 
table, is saturated with air. The spaces between the soil par- 
ticles are completely filled with this ground-air, or soil-air, 
as it is often called. Each soil particle above the water table 
is surrounded by a thin film of water, film water, which can 
be removed only by the roots of plants and by evaporation 
(Art. 13). Since this moisture can be removed by evapora- 
tion, the soil-air will constantly be nearly saturated with mois- 
ture. Plant life is largely dependent upon this moist soil-air 
and upon the film water for its very existence (see Art. 470). 
The chief purpose of artificial drainage is so to lower the water 
table that the soil-air may reach the plant roots. 

461. Movements of Soil-air. — The soil-water moves through 
the soil chiefly through the influence of its own weight; ive 
say it is moved by gravity. It is constantly moving down hill 
toward the sea level or toward the level of some lake or river. 
The movements of soil-air are strikingly different. Soil-air 
does not move, to any considerable extent, as a result of its 
own weight Its motion is controlled almost entirely by: (1) 
Changes in the temperature of the soil, (2) changes in atmos- 
pheric pressure (see Chap. Ill, Sec. II), and (3) by diffusion. 

462. How Heat Causes Movements of Soil-air. — We know 
that when air is heated it expands. In fact, we have learned 
that when air is heated 1°C. it expands H73 part of its volume 



GROUND-AIR 389 

at 0°C. (Art. Ill, Ex. 36) ; if it is heated 15° it will expand 
Wziz of its volume. Now, if the soil temperature should rise 
5°C, it is evident that 1 cu. ft. of air out of every 55 cu. ft. 
would be forced out of the soil, i.e., the earth would exhale, 
or breathe out, 1 cu. ft. to every 2 cu. yd., of soil-air which it 
contained. Prove that this is so. 

The earth receives its supply of energy from the sun. The 
sun sends down a greater amount of energy at noon than at 
any other hour of the day. Why is this so (Chap. IV, Sec. 
I) ? But if we were to take the temperature each hour of 
the day for a few days with the thermometer hanging on the 
north side of a tree or a building, we should find that the 
atmosphere becomes warmest, generally, not at noon, but at 
about two o'clock. Explain this lagging of the hottest hour 
of the day behind the time when the sun sends down its great- 
est heat. (Art. 168.) 

463. Soil Temperatures. — The temperature of 
the soil is most easily taken by means of the soil 
thermometers. These are mercury thermometers 
which are usually encased in wooden cases capped 
With metal tips (Fig. 232). This protecting case 
makes it possible for the thermometer to be pushed 
into the soil without danger of its breaking. Re- 
peated experiments show that at the depth of 1 or 2 
ft. the soil reaches its highest temperature late in 
the afternoon or in the evening. At a still greater 
depth, the soil reaches its highest temperature dur- 
ing the early portions of the night. The change 
in temperature lessens rapidly as greater depth 
is attained, until at a depth of a few feet, no ap- 
preciable daily change is noticeable. It can also 
easily be shown that the soil at the depth of 1 or 2 
ft. reaches its lowest temperature during the day SoUther- 
time, usually during the forenoon. This is not mometer. 
mysterious ; it is simply the application of the prin- 
ciple referred to in the last paragraph. If the changes in 



390 



GROUND-WATER AND GROUND-AIR 



temperature of the atmosphere lags two hours behind the sun, 
we can easily see that the changes in temperature of the soil 
should lag still further behind. 

464. Earth's Breathing. — We have seen that the soil be- 
comes warmest during the evening and earlier portion of the 
night. As long as it is growing warmer, the soil-air is ex- 
panding and therefore rushing out. This is the earth's 
exhalation. The soil-air which is expelled is warm, often 
warmer than the air above ground, and saturated with mois- 
ture. The formation of dew is partly because of this warm, 
moist air's coming into contact with the colder bodies close to 
the surface of the ground (see Art. 183, page 167). The 
earth 's inhalation takes place in the early morning and the 
forenoon. Thus we see that the earth takes one long, slow 
breath each day. 



M» 




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AoX. 





A 







S/o6 




A*7 

(tit. 



Fig. 233. — Effect of pressure upon 
volume of air. 

465. Effect of Pressure upon the Volume of Air. — But the 

change in the soil temperature is not the only cause of the 
earth's breathing. Changes in the pressure of the atmos- 
phere, atmospheric pressure (Chap. Ill, Sec. II), also af- 
fect the soil-air. 

It is easily proved in every high school laboratory that in- 
creasing the pressure upon a certain quantity of air decreases 
the volume of the air. In fact, it was shown by an English 
philosopher, Robert Boyle, about 1650, that, if the pressure 
was doubled, the volume of the gas was reduced one-half; if 
the pressure was made four times as great, the volume became 



GROUND-AIR 391 

one-fourth its former value. In general, the volume of a gas 
decreases just as rapidly as the pressure increases. Figure 
233 makes plain the operation of this law, which is known as 
Boyle's law. .We shall suppose that No. 1 represents a tube 
4 ft. long. At its top, fitting into it air-tight, is a piston. 
Suppose that all of the atmospheric pressure is removed from 
the piston and simply a 1-lb. weight is placed upon it. Evi- 
dently the 4 ft. of air in the tube is supporting 1 lb. of weight. 
If the pressure be increased to 2 lb., the volume of gas will be 
compressed to a volume 2 ft. in length, as in No. 2. If 4 lb. 
of pressure be place.d upon the air as in No. 3, the column will 
become 1 ft. And so 8 lb., 16 lb., 32 lb., 64 lb., and 128 lb., 
will compress the air to 6 in., 3 in., 1% in., % in., and % in., 
respectively. 

466. Changes in Atmospheric Pressure Cause the Earth 
to Breathe. — We have seen (Chap. Ill) that the atmospheric 
pressure varies considerably from day to day, and that it even 
varies somewhat from hour to hour. At the time of storms 
the pressure is often considerably less than on the day before 
or upon the day following. This variation frequently amounts 
to %o of the entire pressure of the atmosphere. Generally, 
however, the change is less than this. 

Now, if the soil-air is relieved of Yso of the pressure which 
it has been sustaining, it will expand % in volume, accord- 
ing to Boyle's Law. This means that Vw of the soil-air will 
be expelled from the soil. After the storm has passed and 
the atmospheric pressure has again increased, fresh air again 
enters the soil. Since on the average, fairly well-marked 
storms pass over central and eastern United States about 
once every four or five days, it follows that the earth takes an 
additional breath, or rather an extra breath, about once in 
four or five days. 

467. Another Cause of Change in Soil-air. — While ,it is 
true that both the changes in soil temperature and the changes 
in atmospheric pressure cause the changes in soil-air as shown, 
it is also true that they are not the only, nor even the chief 



392 GROUNDWATER AND GROUND-AIR 

causes of the exchanges of soil-air which take place. Experi- 
ments have shown that a still more important cause of this 
exchange is that of diffusion. 

Exercise 76. — Diffusion of Gases 

Close all the windows and doors of the room. Open a bottle of 
the oil of peppermint or musk (camphor or ammonia will do) in 
one corner of the room and let a few drops fall upon the floor. 
Let another person be at the opposite corner of the room. Let 
him notice carefully to see how long it is before he can detect the 
odor of the liquid you are using. It will not be very long before 
he can do so. How does it happen that he can thus detect the 
presence of the liquid so distant from him? 

Explanation. — Evidently the liquid does not reach him. 
It must be that it first changed to a vapor, or gas, and that the 
gas by some means reaches him. The truth is that all gases 
are made up of many rapidly moving particles. The parti- 
cles of air, for instance, under the usual conditions of tem- 
perature and pressure are known to. be moving, on the average, 
at the rate of about % mile per second. But the particles 
are so very small and so very numerous that even at this 
rate of motion no particle moves more than a very small por- 
tion of an inch before striking another particle and being 
turned off in some new direction. Every gas and every vapor 
is thus made up of millions of particles to each cubic inch and 
each of these pa'rticles is moving with great speed: When we 
know this to be true, it is not wonderful that' the vapor from 
the musk or oil of peppermint quickly passes across the room, 
even though there be no apparent movement of the air in the 
room. The md'xing of gases and vapors in this manner is 
known as the diffusion of gases. 

468. Diffusion of Soil-air. — It has been shown that this- same 
diffusion of gases applies to soil-air. It is known that this 
diffusion of the soil-air causes a constant exchange to be tak- 
ing place between the soil-air and the air above the ground. 
Particles of soil-air are constantly escaping into the atmos- 



CONSERVATION OF SOIL MOISTURE 393 

phere and particles of fresh air from the atmosphere are con- 
stantly entering the soil. This diffusion of the soil-air causes 
more of an exchange of the impure, moisture-laden air for 
fresh air from the atmosphere than all other known causes put 
together. The whole process of change of soil-air is of great 
interest to agriculturists and is called the aeration of the 

SOIL, or AIRING OP THE SOIL. 

The soil-air removes considerable moisture from the soil 
above the water table. The soil-air is constantly more or less 
saturated with moisture which it has taken up from the soil 
particles. With each exhalation, as well as by the constant 
process of diffusion, this moist air is being replaced by the 
dried air from the atmosphere. The effect of soil aeration, 
then, is to reduce the amount of soil moisture. 

Soil aeration and the consequent drying out of the soil is 
due, then, to three causes : 

1. Changes in soil-air temperature, 

2. Changes in atmospheric pressure, 

3. Diffusion of soil-air. 

III. CONSERVATION OF SOIL MOISTURE 

469. Plant Life and Moisture. — All plants must be sup- 
plied with moisture in order that they may live and grow. 
The abundance or scarcity of moisture is a large factor de- 
termining the character of plant life in any region. Dif- 
ferent plants require different amounts of moisture. Certain 
plants, such as water lilies, reeds, cat -tails, eel grass, bulrushes, 
wild rice, sedges, and many grasses live and thrive only when 
growing in shallow ponds or swamps or marshes. Such plants 
are said to be water plants, or hydrophytes (hydrophyte 
meaning water plant). 

At the opposite extreme are plants which live and thrive 
only when growing in extremely dry soil in regions of scant 
rainfall. The southwestern portion of the United States, 
western Texas, New Mexico, Arizona, and southeastern Cali- 
fornia, is such a region. Here the various forms of the cactus, 



394 GROUND- WATER AND GROUND-AIR 

the yucca, sage brush, and a few other forms of plant life 
live and thrive although only a scanty amount of moisture is 
available. Such plants are called xerophytes (pronounced 
ze'ro-fites, xerophyte meaning dry plant). 

Most of the common plant life of the United States, and 
especially our common cultivated crops require a medium 
amount of moisture. Our common forest trees, the grasses of 
our meadows, our corn, oats, wheat, and other grains, potatoes; 
beans, peas, and all the rest of our common field and garden 
plants thrive best where a moderate amount of moisture is 
available. Such plants are called mesophytes (mesophytes 
meaning middle plants). 




Fig. 234. — Root hairs — on corn 
roots and on roots of wheat. The 
soil is still clinging to the wheat 
root hairs. 

470. How Plants Absorb Soil Moisture. — Plants requiring 
but little moisture, xerophytes, and plants requiring a medium 
amount of moisture, mesophytes, obtain their supply of mois- 
ture principally by absorbing the film moisture from the soil. 
Their roots are often finely branched or divided and the small 
rootlets are covered with minute hairs (Fig. 234). These root 
hairs come into close contact with the film of water surround- 
ing the small particles of soil and absorb the moisture from 
this film as it is needed for plant growth. As the moisture 
in the film is thus absorbed, more moisture rises from the 
deeper portions of the soil to take the place of the absorbed 



CONSERVATION OF SOIL MOISTURE 395 

moisture. This moisture rises, in the same manner and for the 
same reason as kerosene rises in the wick of a lamp. It is said 
to rise on account of capillarity. 

471. Need of Increasing and Conserving Soil Moisture. — 
In most regions, the soil contains sufficient moisture in the 
spring and the early part of the growing season. But in 
many regions the supply of soil moisture becomes too scanty to 
insure the most rapid growth and full development of plant 
life later in the season. In most portions of the United States 
the farmer, gardener, and fruit grower find it desirable so to 
prepare the soil in the fall or spring as to increase its capacity 
for moisture and also to conserve the soil moisture as far as 
possible during the growing season. 

472. Increasing the Capacity of Soil for Moisture. — The 
capacity of soil for holding moisture depends upon several 
conditions. In regions where the rainfall is likely to be defi- 
cient, during the growing season, it is of the greatest im- 
portance that the soil be so prepared as to increase as much 
as possible its capacity for holding moisture. There are 
several ways in which the capacity of the soil may be in- 
creased : 

1. Its capacity may be increased by fall plowing. A con- 
siderable portion of the annual precipitation in many regions 
occurs during the winter months. If the surface of the soil 
is left hard, smooth, and compact in the fall, much of the 
winter precipitation will run off the surface and never enter 
the soil. Fall plowing leaves the surface of the soil loose and 
open, rough and broken, thereby tending to prevent the loss 
of this moisture. 

2. By increasing the amount of humus (Art. 309) in the 
soil, the capacity of the soil for holding moisture is greatly 
increased. Scarcely any other kind of soil has equal capacity 
for holding moisture. 

3. The capacity for holding moisture is greatly increased 
in most soils by providing good under drainage. Well- 
drained soils remain porous while soils not well drained be- 



396 GROUND- WATER AND GROUND-AIR 

come hard and solid. The rainfall readily enters porous soils 
and passes down through such soils to the water table (Art. 
455) below. 

473. How Moisture May be Conserved. — As we have seen 
(Art. 468), at best, considerable soil moisture is evaporated 
and passes into the atmosphere on account of soil aeration. 
Moreover, many soils, when dry, tend to become hard and 
solid, and shrink. The result is, frequently, that cracks open 
in the surface soil. Sometimes these cracks are numerous, 
wide, and deep. Such cracks permit freer circulation of air 
through the soil and consequently more evaporation takes 
place; worst of all, such evaporation takes place at consider- 
able depth. This evaporation greatly lessens the amount of 
film water within the reach of the plant roots. 

Loss of soil moisture through evaporation may be lessened 
by covering the soil with mulch. This mulch may be pro- 
vided by either of two methods : 

1. By the application of a coat of manure, straw, dead 
grass, or any similar material. Mulch of this nature is dif- 
ficult to obtain in sufficient quantities for use on large culti- 
vated fields. 

2. By the preparation of soil mulch. A soil mulch con- 
sists simply of a layer of finely pulverized soil. This is pro- 
duced by thorough tillage after every rain. If the top 1 or 
2 in. of soil is kept in a finely pulverized condition, loose and 
open, during the growing season, the loss through evaporation 
from the surface is greatly reduced. It does this by breaking 
the capillary action at the lower surface of the loose soil. The 
soil moisture rises readily to that point but does not rise 
farther. It is much the same condition we should have in 
our kerosene lamp were the wick cut in two a short distance 
down in the wick tube of the burner. Keeping the surface of 
the soil covered with this soil mulch is the only practical 
method of preventing excessive evaporation from large cul- 
tivated fields. "What effect will such mulch have upon the 
cracking of the soil ? Explain. 



RELATION OF GROUND-WATER TO WELLS 



397 



IV. RELATION OF GROUND-WATER TO WELLS 

474. The Fallacy of Underground Streams. — By many 
people it has been supposed that to "strike a vein of water " 
when boring a well means that the drill has tapped an 
underground stream. "While it is true that underground 
streams exist in some places, the supposition that most wells 
tap something that may properly be called an underground 
stream is false. 




Fig. 235 — An underground stream in limestone. The carbonic acid 
has dissolved the limestone and the ground-water drains away in a true 
underground stream. 

We have already seen that all of the free ground-water 
moves slowly through the soil down hill, or toward a lower 
level. In many places the nature of the soil is such that 
through certain strata, or layers, the water moves more 
rapidly than through others. If a layer of coarse gravel 
and sand slopes down hill, the ground-water passes much more 
rapidly through it than it does through the layers of fine clay 
above and below the gravel. But this would scarcely be called 



398 



GROUND- WATER AND GROUND-AIR 



an underground stream ; it certainly is not what most people 
mean by that term. 

The term "underground stream" may properly be applied 
only to those comparatively rare cases where the water has 
dissolved portions of the rock, washing the dissolved portion 
entirely away and leaving an open channel through which the 
water flows (Fig. 235). But such conditions are so rarely 
found that the underground stream is not of any importance 
when considering the source of water supply for wells. 

475. A Vein of Water. — If to "strike a vein of water" 
does not mean the tapping of an underground stream, what 
does it mean? In meeting this question we shall also be 
meeting the question, What is the real difference between a 
good well with plenty of water and a poor well yielding but 
little water ? 




Fig. 236. — A vein of water. 

In Art. 456 we saw that the relation of the water table to the 
land surface has been determined by noting the height of 
water in wells. "We have also seen that the water in a shallow 
well will stand at exactly the height of the water table, pro- 
vided that no water is used from the well. Why should using 
water from the well affect the height of the water in the 
well? If the well is sufficiently deep so that its bottom is 
below the level of the water table, why should not the well 
contain a sufficient supply of water at all times ? The answer 
to these questions is this: Although the well does reach be- 
low the water table we cannot expect much of a flow till we 
reach a "vein of water." But what is a vein of water? 



RELATION OF GROUND-WATER TO WELLS 399 

It is certain that it is rarely, almost never, an underground 
stream. 

"When a vein of water is struck, it is always found in a layer 
of sand and gravel, or some other open, porous soil; it is 
always a layer which allows the ground-water to percolate 
easily through it. Figure 236 represents an ideal case. The 
soil above and below the bed of gravel, A, is so fine in texture 
that water passes through it slowly. Therefore neither well 
No. 1 nor well No. 2 receives w T ater freely from it. But the 
gravel bed, or gravel pocket as the geologists call it, in- 
creases immensely the exposed surface of the well. This 
pocket of gravel performs exactly the same function for this 
well No. 1, as the infiltration-gallery performs for the well 
in Fig. 231. Well No. 2 would evidently have to be extended 
till it reached gravel bed, B, before it could be supplied with 
water from any other source than from the clay. It is evi- 
dent, then, that a vein of water is merely a vein of sand or 
gravel, porous soil, through which the ground-water percolates 
rapidly. The trouble with a poor well is that it is sunk in 
clay or other materials through which water moves but slowly. 
When water is removed from the well the water nearest in the 
soil soaks into the well and it too is removed. If the pumping 
continues long enough the water table about the well is lowered 
as shown about well No. 2, Fig. 236 ; in fact, the water table 
may be lowered to the very bottom of the well. This could 
not take place if the well were sunk in soil which was suf- 
ficiently open and porous so that water flows readily through it. 

476. Witching for Water. — It has not been long since it 
was common to find people who believed that a vein of water 
could be located by use of a divining rod. In almost every 
community some person could be found who honestly believed 
that he could, by using the divining rod of a favorite wood 
and shape, actually determine the location of an adequate 
supply of underground water. If asked to give a good, 
scientific reason for the fact that the stick turned down- 
ward in his hands as he walked over the supposed vein of 



400 GROUNDWATER AND GROUND- AIR 

water, he was invariably unable to do so but insisted that 
experience proved it. He drew his conclusion from the fact 
that wells sunk in accordance with the behavior of the divin- 
ing rod seldom failed to bare water. 

We have already seen that every well which extends below 
the water table is certain to contain some water and that the 
efficiency of the well depends upon its tapping a bed, or 
pocket, of loose, porous soil through which water may perco- 
late readily. Unless some reasonable connection can be shown 
to exist between the divining rod and the bed of gravel buried 
deep in the soil, "witching for water" must be classed with 
the outgrown superstitions of the past. 

477. Deep Well Water. — Wells are usually divided into two 
classes, surface wells and deep wells. In speaking of wells 
as "surface wells" we do not mean that they are necessarily 
shallow wells. We mean simply that they are fed by the 
surface water, that is, by the ground-water near the surface 
of the earth. In speaking of "deep wells" we mean that such 
wells are fed from deep-seated veins of water. The water 
which enters the surface wells has not usually passed through 
much soil. It is water which has fallen as rain or snow near 
the well ; it has sunk into the ground, joined the ground-water Y 
and found its way more or less quickly into the well. 

The veins of deep-seated water, on the other hand, are sepa- 
rated from the surface waters by layers of nearly impervious, 
clay or other material. Their source of supply is usually at 
considerable distance from the well, often even hundreds of 
miles. They are often rock waters, that is, water which has 
collected in porous layers of rock, such as sandstone. It is 
easily seen, therefore, that local rains can make but little- 
difference in the height of water in deep wells. Most well 
water contains considerable mineral matter in solution; this 
mineral matter produces a whitish curdy material when 
mixed with soap. Such water is called hard water. 

478. Artesian Wells. — By artesian wells we mean deep 
wells. In most cases the water rises above the surface of the- 



RELATION OF GROUND-WATER TO WELLS 



401 



ground. Such wells tap veins of water which usually, not only 
have their source at a great distance from the well, but also 
at a higher level. The water-bearing material lies between 
impervious layers of clay or shale, or at least has such a layer 
overlying it. This overlying layer of clay or shale, tends to 
prevent the water from rising, no matter how great the pres- 
sure upon it. Figure 237 illustrates the layers of rock, which 
underlie South Dakota. 




Fig. 237. — Geologic section from the Black Hills eastward across 
South Dakota. The illustration immensely exaggerates the vertical 
distance as compared with horizontal distance. 

Throughout the eastern half of South Dakota there are 
numerous artesian wells. These wells receive their supply 
of water from a layer of sandstone, known to geologists as 
"Dakota sandstone." This sandstone comes to the surface 
at the eastern edge of the Black Hills. Much of the water 
which falls upon these hills soaks into this sandstone and then 
passes through this porous sandstone down the slope toward 
the east. Since the sandstone comes to the surface at about 
3000 ft. above the sea level and since the surface of the land 
in the eastern portion of the state where the artesian wells 
are so numerous is less than 2000 ft. above the sea level, we 



402 



GROUND-WATER AND GROUND-AIR 




Fig. 238. — Artesian well at Woonsocket, South Dakota. 



RELATION OF GROUND- WATER TO WELLS 403 

should expect the water to rise above the surface of the land. 
From many of these wells the water issues with great force, 
sometimes with a pressure of nearly 200 lb. to the sq. in. 
Figure 238 is a reproduction of a photograph of a well at 
Woonsocket, South Dakota, showing a 3-in. stream which 
rises to a height of nearly 100 ft. The water exerts a pres- 
sure of about 135 lb. to the sq. in. when the pipe is closed so 
as to prevent the escape of the water. 



CHAPTER X 
WATER SUPPLY AND SEWAGE DISPOSAL 

I. THE VALUE OF WATER 

479. Man's Dependence upon Water. — When we read now- 
adays that ' ' a house has modern conveniences ' ' it means that 
it is not only provided with modern appliances for lighting 
and heating, but also that the house is supplied with water 
and suitable plumbing for the disposal of sewage. This is 
especially true of city houses and is becoming more and more 
true of country and farm houses. While we may be quite 
comfortable without having the water piped into the house, 
we must have a sufficient supply of wholesome drinking ivater 
close at hand. 

A supply of wholesome water is much more important to 
man than is artificial light. It is also true that in all but 
severe winter weather and in the colder portions of the 
country, man can live much longer without food or artificial 
heat than he can without water to drink. 

480. Man Has Always Recognized His Dependence upon 
Water. — From the earliest antiquity, man has recognized the 
importance of securing an ample supply of wholesome water. 
Most of the great cities and nations of the past have been 
located upon rivers or lakes containing fresh and wholesome 
water. If the natural water supply was not sufficient, great 
aqueducts were built to bring a supply from a distance and 
huge reservoirs were constructed to store a supply in times 
of plenty. Some of the greatest structures erected by an- 
cient man were these great stone aqueducts and reservoirs 
(Fig. 239). . 

Recognizing their dependence upon water, campers and 
hunters always make camp, when possible, near some spring 
or stream. For a similar reason the earliest settlers of the 

404 



THE VALUE OF WATER 



405 



Mississippi valley and of the great plains to the west settled 
first upon the lands bordering the streams. When all of the 
land bordering the streams was taken and the settler was 
obliged to take land farther back, the first improvement he 
made was to dig a well, for he mnst have water. 

481. Water Valuable for Purposes Other Than Drinking. 
— Streams and other bodies of water have always been the 
highways for commerce. Until the invention of the locomotive 




Fig. 239. — Aqueduct of Segovia, Spain. Nearly one-half mile in length. 
Over 1800 years old. From History of Sanitation, Cosgrove. 

and the perfection of the modern railroad, which have taken 
place within the last century, the means of transportation by 
land were very poor and costly; in fact, there had been 
scarcely any improvement in modes- of travel since the dawn 
of history. The ox and the horse were but little improve- 
ment over the equally rapid-moving camel, which was the 
beast of burden in the earliest Biblical times. For this reason 
practically all of the world's commerce up to about a half- 
century ago was carried on by water. 



406 WATER SUPPLY AND SEWAGE DISPOSAL 

For centuries, man has used the power of running water to 
help him perform his labor. It has ground his corn and 
wheat; it has sawed his lumber and run his looms when no 
other force was available. 

Plant life as well as animal life is largely dependent upon 
water for its very existence. From prehistoric times man has 
used water from near-by streams to irrigate his crops. Some 
of the greatest nations of the past have lived on soil where the 
natural rainfall was insufficient, and artificial watering or irri- 
gation was necessary. 

In each of these cases to which we have been referring, 
man has made use of the visible supply of water, i.e., the 
water which stands or flows above the surface of the land. 
"We have seen, however, that the ground itself is a great 
reservoir of water and that to this vast supply of hidden water 
man owes as much, possibly, as he does to the visible 
supply. 

II. WATER SUPPLY FOR FARMHOUSE AND COUNTRY HOME 

482. New England Well-sweep and the Oaken Bucket. — 

The earliest settlers of New England had little difficulty in 
securing a sufficient supply of good water. Springs are num- 
erous throughout New England. In many localities most 
farmhouses are supplied with water brought in pipes from 
nearby springs. Many villages and towns also receive their 
supply from springs or hillside brooks fed by springs. Where 
the water does not come to the surface, it is nearly always 
easily obtained by digging shallow wells. These wells are 
often not more than 10 or 15 ft. deep. 

In the days of the colonies the usual method of raising the 
water from •these shallow wells was by means of the well- 
sweep and the oaken bucket. A heavy weight was fastened 
to the short end of the long«sweep to balance the long arm of 
the sweep. The lifting of the bucket full of water thus be- 
came an easy task. This method of raising water from a 



WATER SUPPLY FOR FARMHOUSE AND COUNTRY HOME 407 



well has been immortalized in the familiar song "The Old 
Oaken Bucket." 

483. The Suction-Pump. — Water for household and farm 
use is usually lifted out of moderately deep wells by suction- 
pumps. A common suction-pump con- 
sists of two parts, the pump-head, and the 
pump-run. When made of wood, the head 

is usually from 6 to 8 in. square and about 
7 or 8 ft. in length. This head is hollow, 
that is, a hole 3 or 4 in. in diameter is bored 
throughout its length (Fig. 240). Into 
the lower end of the head a metal tube, the 
cylinder, is fitted. The cylinder is made 
smooth and true on its inner surface ; when 
of iron it is often lined with enamel. Fit- 
ting closely into this cylinder is the plunger 
or bucket. This plunger or bucket, carries 
the plunger-valve which opens easily up- 
ward but which prevents any water above 
it from passing downward. The plunger 
is raised and lowered by means of the 
plunger-rod, attached to the pump-handle. 
Fitting closely into the lower end of the 
head is the pump-run, or the suction- 
pipe. In the common wooden pump this 
run is about 4 in. square and has a hole about IV2 o r 2 in. 
in diameter bored throughout its length. At the lower end 
of the cylinder, below the plunger, is a second valve, the 
inlet -valve. This valve also permits the water to pass up- 
ward but prevents a downward flow. 

484. How the Suction-pump Works. — The way in which 
the suction-pump works is made clearer by studying the 
sketches of the common cistern pump (Fig. 241). As the 
handle is forced downward, the plunger rod and plunger are 
raised. The water which is already above the plunger, or 
bucket, is lifted till it stands higher than the spout, out of 




PUMP 
RUN' 



Fig. 240.— The suc- 
tion pump. 



408 WATER SUPPLY AND SEWAGE DISPOSAL 

which it runs. But what raises or lifts the water in the run 
and cylinder below the plunger? We say it is raised by 
suction, or that it is sucked up (see Art. 284). 

In the suction-pump, as the plunger is raised there is a 
tendency to produce a vacuum just beneath it. The atmos- 
phere pressing down upon the surface of water in the well 
forces the water up the run and through the inlet-valve to 
fill the vacuum. The work we do, then, in pumping with the 
suction-pump is really expended in lifting the small amount 
of water in the pump-head already above the plunger and in 
lifting the atmospheric pressure which is pressing downward 




Fig. 241. — Common iron cistern pump. 

upon the surface of that water, and not in pulling or drawing 
the water up the pump-run. Define suction and sucking 
(Art. 284). Explain the process of ' 'sucking' ' soda water up 
a straw. 

485. Lift-pump. — A lift pump is constructed exactly like 
the head of a suction-pump. Were the head of a suction- 
pump long enough to reach to the bottom of the well, it 
would become a lift-pump. The inlet valve, then, is at the 
bottom of the well and the cylinder and plunger are at all 
times below the surface of the water in the well. The water 
is therefore lifted and not sucked up. 

486. The Force-pump. — It is often necessary to raise water 
to a level above that of the pump spout. In farmhouses and 



WATER SUPPLY FOR FARMHOUSE AND COUNTRY HOME 409 



in dwellings in small towns, where there are no city water 
works, it is often desirable that water be pumped into a tank 
in the attic so that sink faucets may.be supplied with water 
under pressure at all times. Unless some such plan is adopted, 
modern plumbing conveniences can not be installed in such 
dwellings; with such a tank, common farmhouses may be 
equipped with most of the conveniences 
of city dwellings. Any pump so con- 
structed that it may be used to force 
water to a height above the pump is 
called a force-pump. 

As far as the lower portion of a 
force-pump is concerned, it may be 
either a suction-pump or a lift-pump. 
Figure 242 shows the construction of 
an iron force-pump. It differs from 
the ordinary iron suction-pump 
only in having a portion of the 
head somewhat enlarged so as to en- 
close a considerable quantity of air, 
forming an air cushion, and in hav- 
ing the opening at the top through 
which the plunger rod passes packed 
air-tight. Explain the use of the three 
valves, A, B, C. 

The air cushion is necessary on all 
force-pumps if we are to secure a fairly 
steady stream from the pump. "With 

each upward stroke of the plunger, the air in the air cushion is 
compressed. While the plunger is descending, this com- 
pressed air, pressing downward upon the water in the pump, 
keeps forcing a steady stream of water through the delivery 
pipe into the tank. 

487. The Pneumatic Tank System. — The convenience and 
comfort derived from having an ample supply of water under 
pressure in a dwelling can be appreciated only by those who 




Fig. 242.- 
pump. 



-The force- 



410 



WATER SUPPLY AND SEWAGE DISPOSAL 



have lived with, and again without, such conveniences. Not 
only can all of the conveniences of modem plumbing be ob- 
tained, but a reasonable protection against fire is thus secured. 



INECTHMEHERE Y ATTIC 

INCASE OF FIRE /J T 



SECOND FLOOR 



P 



iTS 




STOP COCK 



FIRST FLOOB 



CONNECT HOSE HERE 
INCASE OF _„_ .,. 
Fine -^ fiTT KITCHEN 




Fig. 243. — Pneumatic tank system. 

Figure 243 shows how such a system may be installed and the 
conveniences which it makes possible. In such a system the 
tank is placed in the basement of the house, safe from frost 
and easy of access. 



WATER SUPPLY FOR FARMHOUSE AND COUNTRY HOME 411 

The water is raised from the well or cistern and forced into 
the tank by means of a force-pump. The lower portion of the 
tank contains water and the upper portion compressed air. 
This compressed air constantly presses downward upon the 
water in the tank, forcing it into the pipes. Special pro- 
vision must be made to pump more air into the tank occa- 
sionally. If this is not done the tank will in a short time be- 
come "water-logged," that is, all of the air will be removed 
from the tank by the water which passes through it. How 
this may be so is more clearly seen after performing the fol- 
lowing exercise. 

Exercise 77. — Removing the Air from Water 

Place a tumbler or flask filled with water under the- receiver of 
the air pump, first noting the temperature of the water. Begin 
pumping the air from the receiver. While taking the first few 
strokes watch carefully to see if any bubbles are rising through the 
water. Pump out most of the air, watching constantly for bubbles 
of rising air. 

Explanation. — We all know that sugar or salt may be 
dissolved in water ; in much the same way air readily dissolves 
in water. Since the atmosphere is always resting upon the 
surface of water standing in an open vessel, it is always pos- 
sible for air to be dissolved in the water. But is there a limit 
to the amount of air which will be thus dissolved by a given 
quantity of water? We know from experience that there is 
a limit to the amount of sugar or salt which will dissolve in a 
given quantity of water. After the water is "saturated" 
with the salt or sugar, adding more of the solid simply means 
that it will settle to the bottom of the liquid and remain there 
undissolved. In the same way, a vessel of water standing open 
to the air is soon "saturated" with dissolved air; it contains 
all the air it is possible for it to contain under the given con- 
ditions. From Ex. 77 what do you conclude is the effect 
of reducing the pressure of the air upon the surface of the 
water ? 



412 



WATER SUPPLY AND SEWAGE DISPOSAL 



Henry's Law. — The amount of gas dissolved in water is 
directly proportional to the pressure, that is, doubling the pres- 
sure doubles the amount of gas which dissolves in a given 
quantity of water. This law holds true only when there is no 
chemical union between the gas and water, as is the case when 
air is dissolved in water. 

One cu. ft., or 1728 cu. in., of water at 0°C. and at the 
pressure of 15 lb. per sq. in., that which the atmosphere 
exerts at the sea level, dissolves about 45 cu. in. of air. By 
Henry's Law we see that doubling this pressure would cause 
about 90 cu. in. of air to be dissolved in each cubic foot of 
water, or reducing the pressure to 5 lb. to the sq. in. reduces 
the amount of dissolved air to 15 cu. in. per cu. ft. 




Fig. 244. — Why shallow wells are dangerous. 

The need of pumping more air into the tank occasionally 
to prevent it from becoming "water-logged" is now evident. 
The water in the well or cistern is under 1 atmosphere of 
pressure; therefore there are about 45 cu. in. of air in solu- 
tion to each cubic foot of water as it enters the tank. The 
water in the tank is kept constantly under a pressure of, at 
least, 2 atmospheres ; the water, therefore, as it escapes from 
the tank through the pipes and faucets, contains at least twice 



WATER SUPPLY FOR FARMHOUSE AND COUNTRY HOME 413 

as much, air as it did in the well. Evidently, if no additional 
air were pumped into the tank, the tank would soon become 
" water-logged." What would be the result? 

488. Shallow Well Water Often Dangerous.— We have 
seen that wells are supplied by the ground-water. It is evi- 
dent that, if the walls of the well are merely bricked up to 
prevent the walls from caving in, they will not be water tight. 
In such cases surface water, at times of frequent and heawy 
rains, will readily enter the well very near its top. If such a 
well be located near a barnyard on a farm or in a somewhat 
thickly settled portion of a town or city, especially one not pro- 
vided with sanitary sewers, the surface soil about the well will 
be contaminated with manure and other decaying animal and 
vegetable matter. The surface water, at times of heavy rains, 
may enter at the surface or, at best, merely soak a few feet in- 
to the soil before finding its way into the well (Fig. 244). 

Such surface water will necessarily carry with it much un- 
decayed or but partially decayed vegetable and animal matter. 
Such matter later decays (Arts. 304 and 305, Chap. VII) 
rendering the water unwholesome for use and not infrequently 
causing sickness and sometimes death. The danger is great- 
est when the waste matter is from the human body. This is so 
because the waste matter thrown off from the human body is 
very likely to contain microorganisms which cause human 
diseases. Typhoid fever is often caused by drinking water 
containing typhoid bacilli (Art. 359). 

489. Protecting a Shallow Well against Surface Water. — 
All shallow wells should be protected against surface water. 
Some protection is provided by constructing the walls and 
cover of the well water-tight. When the walls and cover of a 
shallow well are water-tight, there is no opportunity for the 
contaminated surface water to get into the well until it has 
percolated through the soil to the bottom of the well. In 
passing thus through the soil, the water is fairly well filtered, 
and the danger of contamination is lessened. 



414 WATER SUPPLY AND SEWAGE DISPOSAL 



III. CITY WATEE SYSTEMS 

490. Privately Owned and City Owned Water Systems. — 

In communities where the families live in homes separated by 
considerable distances, each family must provide its own water 
supply. But as soon as a region becomes thickly settled, it 
becomes somewhat less expensive and in every way better for 
the whole community to be served by a common water system. 
City governments generally maintain such water systems to 
supply all who live within the city limits. Sometimes a pri- 
vate corporation is granted a franchise by the terms of which 
the corporation may lay pipes in the public streets and may 
sell the water to customers under certain conditions and regu- 
lations stated in the franchise. In a similar manner, private 
corporations very frequently are granted franchises to fur- 
nish customers with electric current and gas for lighting, cook- 
ing, and for power purposes, and occasionally to furnish heat 
for heating homes and places of business (Arts. 48 and 64). 
Inasmuch, however, as public health is so largely dependent 
upon a safe, uncontaminated water supply, the water system 
of a city is more commonly controlled by the city government. 

491. Amount of Water Used. — It has been estimated that 
the amount of water used for household purposes in homes not 
supplied with running water or water under pressure is from 
2 to 4 gal. daily per person. The amount of water required 
per person in any city depends upon the occupation of the 
inhabitants. A manufacturing city requires generally a much 
larger supply of water than does a residence city. It is com- 
mon practice to construct water plants capable of furnishing 
from 50 to 80 gal. daily per capita in the ordinary city where 
the demand is not great for manufacturing purposes. In some 
American cities containing many factories and other industries 
requiring large amounts* of water, as much as 100 or even 
200 gal. per capita are required. To furnish such immense 
amounts of water, elaborate pumping and distributing sys- 
tems are necessary. Figure 245 shows a modern pumping 



CITY WATER SYSTEMS 



415 



station for a small city. The pump used is a centrifugal 
pump; it is driven by a gas engine (Art. 603, et seq.) which 
uses gas made from coal as fuel. 

492. Sources of City Supply. — It is often a serious under- 
taking for a city to secure an adequate supply of water of 
such a degree of purity that it may be used safely for drinking 
purposes, that is, in its unboiled, or "raw," state. Many of 
our larger cities are located on rivers or lakes where an 
abundance of water is obtainable. But the purity of such 




Fig. 245. — A modern city pumping station. Three-stage centrifugal 
pump, belt-driven by 150 h.p., three-cylinder gas engine, with suction 
gas producer. 

water is frequently not such as to warrant its use without 
purification. Sometimes sufficient purification is secured by 
pumping the water into a settling tank where most of the 
sediment is removed and then passing it through sand filters 
where most of the finer suspended matter and bacteria are 
removed. Sometimes it is found necessary to treat the water 
chemically in addition to filtering it. This is most frequently 



416 



WATER SUPPLY AND SEWAGE DISPOSAL 



the case when a city gets its water supply from a river into 
which other cities nearer its source have emptied their 
sewage. 




Fig. 246. — Central Square Water Works, 1800. From History of 
Sanitation, Cosgrove. 

493. Development of City Water Systems. — The modern 
city water system has been developed within the last century. 
We shall see in Chap. XI, p. 502, that the steam engine was 



CITY WATER SYSTEMS 



417 



still a very crude machine at the beginning of the 19th cen- 
tury. City water systems were still less well developed. 
Philadelphia was one of the first of American cities to con- 
struct a city water system. Fig. 246 is a section through the 
Central Square water works of that city constructed in the 
year 1800. Its crudeness is evident when compared with a 
modern city water plant. The boiler was constructed of 5-in. 
pine plank with iron firebox and flues. The distributing pipes 
were also of wood, being logs with the center bored out. 
The system was never very satisfactory; the boiler leaked 
steam and the pipes leaked water. In 1804, Philadelphia be- 




( Copyright, Underwood & Underwood.) 

Fig. 247. — The Miraflores Wafer Purification Plant, capacity, 
15,000,000 gallons per day. A large factor in making the Panama 
Canal zone habitable. 

gan laying iron pipes and is believed to have been the first 
city in the world to do so. New York City's water system, 
as well as modern plumbing in America, really dates from the 
completion of the Croton Aqueduct about 1850. 

494. Water System of New York City. — Many of our 
larger cities have spent immense sums of money in obtaining 
an adequate water supply. In 1842, New York City first 
began using water from the Croton Reservoir. An immense 
dam had been constructed across the Croton River forming 



418 



WATER SUPPLY AND SEWAGE DISPOSAL 



the reservoir. An aqueduct, the Croton Aqueduct, conveyed 
the water to the city. In 1890 this water system was en- 
larged. The cost of the Croton Aqueduct and Reservoir 




Fig. 248.- 



-Philadelphia high-pressure fire service, 
made in underwriters' test. 



Vertical stream 



is said to have been $160,000,000 and the labor required in 
their construction was equal to that of 600 men working for 
10 years. In spite of the immensity of the Croton supply, 



CITY WATER SYSTEMS 



419 



about 500,000,000 gal. daily, the city is outgrowing its water 
system. At the present time a second source of supply is near- 




Fig. 249. — Plumbing in a modern city dwelling. 

ing completion. The city acquired possession of an area of 
900 sq. miles of mountainous land in the Catskill Mountains 
and is constructing an aqueduct to bring the rainfall of 



42,0 



WATER SUPPLY AND SEWAGE DISPOSAL 




Fig. 250. — The water supply of New York City. 



CITY WATER SYSTEMS 421 

that region to the city (Fig. 250). The new aqueduct is 127 
miles in length. The water is carried through a tunnel over 
4 miles in length and at a depth of 1100 ft. beneath the 
Hudson River and later through another tunnel at the depth 
of 700 ft. beneath the East River. It is estimated that the 
new system will cost $200,000,000 and that it will double the 
city's water supply, making the supply 1,000,000,000 gal. 
per day. This will be an ample supply for a city of 8,000,000 
population, allowing 125 gal. a day per capita. Every effort 
is being made to safeguard the purity of the water from the 
new source. To do this, seven villages in the Catskills have 
been abandoned. At the completion of the Catskill develop- 
ment the city will have expended nearly $100 per capita for 
its water supply. 

495. City Supply from Deep Wells. — Many of our smaller 
cities are able to obtain a sufficient supply of water from deep 
wells. Many of the cities of southern Wisconsin and north- 
ern Illinois, for example, obtain their water from a layer of 
sandstone which comes to the surface in northern Wisconsin 
but which is generally reached at a depth of 1000 ft. or more 
in Illinois. The source of this water supply is at a somewhat 
higher elevation; therefore, many of these wells are flowing 
wells. London, Eng., and Brooklyn, N. Y., have in the past 
secured a considerable portion of their water supply from 
wells. 

496. City Water Must be under Pressure. — The city is 
fortunate which has its source of supply at a considerable 
elevation above the level of the city. It is necessary that the 
city supply shall be under pressure, not only in order that 
the water may be used on the upper floors of tall buildings, 
but also to aid in the fighting of fires. It is also of great 
service that the water be under pressure in a city, for it may 
then be used for power purposes (Fig. 248). Water motors 
are frequently used where small amounts of power are occas- 
ionally used as in running the family washing machine. All 
modern plumbing is constructed to be used in connection with 



422 



WATER SUPPLY AND SEWAGE DISPOSAL 



a water system where the water is under considerable 
pressure. 

Figure 249 shows the arrangement of the plumbing in a 
modern city dwelling. It will be seen that both city water 






A 

Fig. 251.— City fire hydrant. 

and soft, or cistern water, are provided. The city water 
being under pressure is made to pump the soft water into the 
storage tank in the attic. The hydraulic pump by which 
this is accomplished is generally called a water-lift. One- 
half of the water-lift, the left half in the figure, is really a 
water motor operated by the city water; the other hal 



CITY WATER SYSTEMS 



423 



is a pump operated by the motor and it pumps the cistern 
water. 

497. The Fire Hydrant. — In cities, fire hydrants are at- 
tached to the city main at frequent intervals. Fire hose can 
be attached quickly to the fire hydrant at the connection near 
the top of the hydrant (Fig. 251). By opening the cutoff 
valve the full pressure on the city main may then be utilized 
in fighting fire. A, Fig. 251, shows the position of the valve 
when the city pressure is cut off the hydrant; B, Fig. 251, 
shows the position of the valve when it is open and the city 
pressure is on the hydrant. The 
valve is controlled by a rod extend- 
ing from the top of the hydrant to 
its bottom. A screw thread is cut 
on the rod opposite the point where 
connection is made to the city 
main. The upper half of the 
thread is left-handed, the lower 
half is right-handed. The upper, 
left-handed thread carries a left- 
handed burr; the lower, right- 
handed thread carries a right- 
handed burr. To these burrs are 
attached short rods or levers which 
control the valve. When the valve is to be opened, a wrench 
applied to the projecting portion of the rod at the top of the hy- 
drant is turned counter-clockwise. This revolving of the rod 
forces the upper burr upward and the lower burr downward. 
The levers spread as the burrs separate and the valve is drawn 
back away from its seat, thus permitting the water from the 
main to rush into the hydrant. 

498. The Water Pressure-gage. — Water pressure is usu- 
ally indicated by pressure-gage. The pressure-gage con- 
sists essentially of an elliptically shaped, thin-walled tube 
bent into a nearly circular form (Fig. 252). When the pres- 




Fig. 252. — Pressure-gage. 



424 WATER SUPPLY AND SEWAGE DISPOSAL 

sure within the tube increases, the tubes tend to straighten 
out. This motion is transmitted to the pointer which moves 
over the face of the dial. The mechanism is so adjusted that 
the instrument shows directly the pressure per square inch. 
499. The Water Meter. — While the pressure-gage is a 
necessity at the pumping station indicating to the engineer 
the exact pressure on the city mains, the majority of con- 
sumers are more concerned with the water meter. The pres- 
sure-gage merely indicates the pressure under which the 
water is kept; the water meter indicates the number of gal- 
lons or cubic feet of water which flow through the pipes. 




Fig. 253. — Interior view of a Water Meter. 

Generally, the consumer pays for the amount of water con- 
sumed, no account being taken of the pressure maintained. 
This is so, notwithstanding the fact that it requires more 
work (see Art. 555, and Chap. XI) and costs much more to 
pump the same number of gallons of water into the city 
mains when a high pressure is maintained than it does when a 
low pressure is-maintained. 

500. Construction of the Water Meter. — There are water 
meters of many different forms, but most small meters are of 
the form known as the disk type. The only moving part in 
the measuring chamber is a hard rubber disk. This disk is 
borne, at its center, on a small sphere of the same material. 



CITY WATER SYSTEMS 425 

The case of the meter is usually constructed of bronze so that 
it will not rust or corrode. The measuring chamber is of the 
shape of the central portion of a sphere (Fig. 253). As the 
water passes through the meter, it causes the disk to move 
with what is known as nutation motion (nutation from a 
Latin word meaning nodding). The center of the rubber 
sphere is the point about which the disk moves. If we were 
to place a common wagon wheel upon the ground so that it 
rests upon its hub and we were then to walk around the wheel 
stepping upon its tire, we should be giving the wheel a 
nutation motion. The upper end of the hub would move 
with a nodding motion as seen from one side. The water 
flowing through the meter produces just this sort of motion 
in the disk. The disk at all times divides the measuring 
chamber into two separate and equal-sized chambers. A cer- 
tain amount of water passes through the meter for each com- 
plete nutation of the disk. Projecting above the disk at its 
center is a pin which rests against a short horizontal lever. 
As the disk rotates, or rather nutates, thi§ lever is carried 
around and around. A train of gears transmits this motion 
to the dials, thus recording the amount of water which flows 
through the meter. 

501. Water Meters Generally Reliable. — A good meter is 
long lived and usually records the amount of water used fairly 
accurately. If in error it is generally owing to wear. In 
that case the meter will likely register too small an amount 
of water because some slips past the disk without causing it 
to rotate. Water users sometimes complain of the meter's 
reading too high. If a meter reads correctly when first in- 
stalled, it is almost certain later to read too low on account 
of wear. Excessively high reading is generally on account of 
some undiscovered leak in the piping or too lavish use of 
water. Leakage is easily discovered, however, by means of 
the test-dial, a pointer which indicates the consumption of a 
cubic foot and fractions of a cubic foot (Fig. 254). To test 
for leakage, close all taps in the building and watch th^. test 



426 



WATER SUPPLY AND SEWAGE DISPOSAL 



pointer for a few minutes. If any serious leakage is taking 
place, the test pointer will be seen to keep moving. 

502. How Water is Sold to the Consumer.— Although 
water is generally sold by the 1000 gal., meters often record 
the amount used in cubic feet. There are 231 cu. in. in 1 
gal., while there are 1728 cu. in. in 1 cu. ft. There are, then, 
nearly 7.5 gal. in a cubic foot. 




Fig. 254. — The straight reading reg- Fig. 255. — The dial register, 
ister. It reads 988,097 cu. ft. It reads 987,997 cu. ft. 

PROBLEM 

If water costs 25 cts. for 1000 gal. and the daily -consumption 
for a city school building is 350 cu. ft., what is the cost of water 
per day? Ans. 65 -(-cts. 



503. Reading the Water Meter. — A water meter may have 
either a straight-reading register or a dial-reading regis- 
ter. The straight-reading register needs no explanation (Fig. 
254). The dial-reading register is so constructed that it re- 
quires a complete revolution of the pointer on any circle to 
indicate the whole number of cubic feet indicated above or 
below that circle. The circumference of each circle is divided 
into tenths. In the illustration (Fig. 255) the highest read- 
ing pointer stands between 9 and 0. The circle is labeled 
1,000,000 cu. ft. The pointer, therefore, indicates a reading 



SANITARY PLUMBING 427 

of something more than 900,000 cu. ft. The next pointer 
indicates a reading of 80,000 cu. ft. ; the third pointer 7,000 ; 
the fourth pointer 900; the fifth pointer 90 and the sixth 
pointer 7 cu. ft. If desired, the number of tenths of cu. ft. 
may be estimated by estimating the position of the pointer 
when it stands between any two figures on the 10-ft. dial. 

Exercise 78. — Reading a Water Meter and Computing the Cost of 

Water 

Kead the water meter at home or at the school on several suc- 
cessive days recording carefully the reading each day. Ascertain 
the price charged for water and compute the cost of each day's 
supply. 

IV. SANITARY PLUMBING 

504. Development of the Art of Plumbing. — The art of 

modern plumbing has been developed within the past half- 
century. The word plumbing is derived from the Latin word 
plumbum, meaning lead. From the early days of plumbing, 
lead pipes have been used to convey water, hence the name 
plumbing has come to be applied to the entire art of supply- 
ing water to buildings and to the disposal of the sewage. 

The Greeks and Romans, especially the Romans, made 
much progress in developing the art of plumbing, although 
many of their efforts would be considered very crude today. 
During the 600 years from 300 b. c. to 300 a. d., the Romans 
built no less than 20 aqueducts, with a total length of 400 
miles, to supply the city of Rome with water. It has been 
estimated that while Rome's population was about 1,000,000, 
still the city was supplied with sufficient water from these 
aqueducts, and from other sources, to permit the use of from 
30 to 100 gal. a day by each inhabitant. To dispose of this 
large amount of water after it had been used, immense 
sewers were constructed, many of which are still in 
use. 

Rome developed the most extensive and luxurious system 



428 



WATER SUPPLY AND SEWAGE DISPOSAL 



of public baths the world has ever known. The public baths 
of Diocletian alone accommodated 3200 bathers at a time; 
the baths of Caracalla, still more famous and luxurious, accom- 
modated 1600 at once. These baths were not free, the usual 
fee being one quadran, the smallest of Roman coins, about the 
equivalent of one-fourth of a cent in our money. The bath 
was not taken by the Roman merely for the sake of health or 
cleanliness; it was regarded as a luxury and was often re- 





Fig. 256. — The 18th century 
hot water system. 



Fig. 257. — The water front and 
its connections with the boiler. 



peated many times each day. The bath was always taken by 
the Romans after exercising and before the principal meal, 
and it has been said that it was frequently taken also after 
the meal in order to stimulate an appetite whereby they 
might eat in a more gluttonous manner. Emperor Nero, who 
reigned during the 1st century, is said to have indulged in 
this practice. Historians often declare that the downfall of 
Rome was partly due to these indulgences which tended to 



SANITARY PLUMBING 429 

weaken the physical strength and vitality of the people. 
Rome was repeatedly invaded and plundered by the fierce 
barbarians from the north and east for two centuries till the 
empire finally came to an end in 476 a. d. During this period 
nearly all the works of art, the bronzes, precious marbles, 
and nearly every other evidence of civilization which had 
been accumulated during centuries were destroyed. The 
famous aqueducts and baths were largely destroyed along 
with the rest. 

505. Hot Water Systems of the 18th Century. — After the 
destruction of Rome, many centuries passed before man again 
paid much attention to the development of the art of plumb- 
ing. In time, however, man again began to think of im- 
proving his conditions for comfortable living. The reproduc- 
tion of an old woodcut (Fig. 256), shows the method of 
heating water in the most fashionable hotels of London in 
the 18th century. The water was pumped by hand into an 
attic tank. By means of an iron pipe it was conveyed down 
again into the bottom of the wrought-iron, riveted boiler at 
the fireplace. Here it became heated. A second iron pipe, 
shown in the illustration, extended from the top of the boiler 
to the guests' rooms. The weight of the column of cold 
water forced the heated water up to the guests' room when- 
ever needed. Thus to be able to have hot water in one's 
room was considered to be a great luxury (Art. 138). 

506. Hot Water System in the Modern Residence. — Today 
no modern residence is complete without a supply of hot 
water. In Fig. 256 it will be seen that one side of the boiler 
was heated directly by the fire. In the modern residence, 
however, the water is heated by circulating through a water- 
back or water-front in the kitchen range, or a heating-coil 
in the furnace, or by circulating through a special heater 
supplied for this particular purpose. 

When the heater forms the front plate of the firebox it is 
called a water-front; when it forms the back plate of the 
firebox it is called a water-back. Figures 243 and 249 also 



430 



WATER SUPPLY AND SEWAGE DISPOSAL 



illustrate the usual manner of connecting the boiler with the 
heater. The arrows in Figs. 243 and 257 show the direction 
of flow of water. Explain why the water circulates as it 
does. What effect does heating water have upon its volume? 
What is the effect upon its density (Ex. 11) ? What is the 
cause of convection currents (Art. 115) ? The circulation of 
water through the heater is just as truly due to convection 
as the circulation of air through a furnace and the furnace 
pipes. Why is it best that the cold water supply pipe should 






ECCENTRIC^ 
BUBBCR CUSHION VALVE CLOSED 

Fig. 258.— The Fuller bibb. Fig. 259.— The self-closing 

compression bibb. 

extend nearly to the bottom of the boiler ? In which portion 
of the boiler is the water the hotter, the bottom or the top? 
Why? 

507. The Faucet or Bibb. — There are many different styles 
of faucets, or bibbs, as the plumber calls them. The Fuller 
faucet is a common type (Fig. 258). The figures show its 
construction and how it works. After being used for some 
time, especially if used on a hot water system, the rubber 
ball is likely to become softened and expanded, thus inter- 
fering with the flow of the water. New balls are easily in- 



SANITARY PLUMBING 



431 



serted by anyone handy with tools. Most types of fancets 
occasionally need slight repair. 

Faucets used in hotels, public places, and especially in 
schoolhouses, are often of the self-closing type (Fig. 259). 
This is a modified form of the common compression faucet. 
As is the case with any compression faucet, a right-handed 
tread on the post lifts the valve from its seat when the handle 
it turned counter-clockwise. But in this faucet a stiff spiral 
spring surrounding the post is thereby compressed. As soon 
as the pressure upon the handle is removed, the spring forces 
the valve down again upon its seat. What is the advantage 
of a self -closing faucet? 




Fig. 260. — An expensively furnished bathroom in 1875. 

Exercise 79. — A Study of Faucets 

Secure from a plumbing bouse as many types of faucets as pos- 
sible and study each carefully, noting its construction and how it is 
operated. Make a sketch of each and write a brief description of 
it telling how it works. 

508. Importance of Good and Sanitary Plumbing. — No 

portion of a modern residence needs to receive more careful 
attention than the plumbing. Faulty or cheaply constructed 



432 



WATER SUPPLY AND SEWAGE DISPOSAL 



plumbing is likely to prove both dangerous to health and, in 
the end, very expensive because no other kind of repair work 
is more expensive than repair of plumbing. In fact, good, 
safe plumbing is considered so important that the laws of 
most states and cities require that all plumbing work be done 
by licensed plumbers who have passed examinations intended 



} :._ : 





t?V- 



Fig. 261. — A modern sanitary bathroom. 



to test their knowledge of sanitary plumbing. These laws 
require that all plumbing shall be constructed in a sanitary 
manner; in many cases they state exactly the way in which 
the plumbing shall be constructed. 

509. Sanitary Fixtures. — Such fixtures as bath tubs, sinks, 
lavatories, wash tubs or laundry trays, and closets have been 



SANITARY PLUMBING 433 

greatly improved within very recent years. Only 30 or 40 
years ago the fixtures used in the most expensively furnished 
residences were very unsanitary as well as very expensive as 
compared with those used today. Figure 260 shows an ex- 
pensively furnished bathroom of about 1875. It was thought 
desirable in those days to conceal all piping and other metal 
work within elaborately carved woodwork. In those days 
such fixtures were not made of single, water-tight pieces as 
they are today. The result was that more or less moisture 
was certain to collect within the wooden cabinetwork sur- 
rounding the fixtures. Such spaces were dark and moist, 
ideal places for the growth and development of microorgan- 
isms. A glance at the cut shows the utter impossibility of 
keeping such a bathroom clean and in a sanitary condition. 

The fixtures used in modern plumbing are strikingly differ- 
ent from those used a few years ago. Figure 261 shows the 
equipment of a modern bathroom. Notice (1) that all these 
fixtures are of one-piece construction, (2) that they are of 
solid porcelain or enameled iron, (3) that they are so raised 
from the floor that the space beneath is light, airy, and easily 
cleaned, (4) that all piping is exposed so that possible leaks 
are easily discovered. Carefully compare the fixtures and 
plumbing of this room with those shown in Fig. 260. What 
advantages do you see in their use? 

510. The Drains. — The drains in any building are of the 
greatest importance, so far as sanitation is concerned. They 
must be so constructed as quickly to dispose of all waste 
matter. They must also be air-tight within the building. 
We have seen that all organic matter is decomposed by 
microorganisms (Art. 305) . These microorganisms attack and 
decompose the waste matter in the drains. During the 
process of decomposition this waste matter often gives off 
large amounts of gases. Many of these gases have offensive 
odors and they are generally regarded as being very un- 
healthful. Some of these gases while nearly without odor 



434 



WATER SUPPLY AND SEWAGE DISPOSAL 



are just as unhealthful. The drains must be so constructed 
as to prevent the escape of these gases into the building. 

To insure air-tight construction all drains within the build- 
ing must be of metal. The larger and straighter pipes are 
generally of iron with all joints closed by means of calking 
with oakum and lead ; the smaller and bent pipes are often of 
lead with all joints wiped, i.e., soldered. 




Fig. 262. — Plumbing in a residence. 

511. Venting the Drains. — The main drain pipe should be 
thoroughly ventilated, i.e., provision should be made whereby 
a current of fresh air passes constantly through the drain pipe 
and out through the soil, pipe (Fig. 262). The air and gases 
within the drain and soil pipe are nearly certain to be 
warmer and less dense than outside air. Explain clearly the 



SANITARY PLUMBING 435 

circulation of air through the drain pipe, and its cause. 

512. The Trap. — Every opening into the drain, whether it 
be from sink, lavatory, bath, or closet should be sealed by 
means of a trap. Most traps consist of a sharp upward bend 
in the drain pipe just after it leaves the fixture. The water 
settles into this bend and seals the outlet. Point out the 
traps in the illustrations. 

Exercise 80. — A Study of Traps 

Examine several fixtures in the schoolhouse or residence and 
study carefully the traps. Notice the provision which is made for 
removing obstacles from the bottom of the trap. Such openings 
are called cleanouts. 

513. Siphoning of Traps. — When a large flow of water 
passes though the trap, it sometimes happens that the water 
completely fills the drain pipe beyond the trap and causes all 
the water to pass over the upward bend, thus leaving the trap 
unsealed. When this happens, the trap is said to have been 
siphoned out. To prevent siphoning, an air vent is usually 
connected at the highest point of the trap, the other end of the 
vent pipe opening either into the soil pipe some distance above 
or opening into the air above the roof (see Fig. 262). 

Exercise 81. — A Study of the Siphon 

Place one end of a small clean rubber tube into a vessel of water 
and hold beneath the surface of the water. Place the other end 
between the lips and suck out the air (see Art. 284). When the* 
tube is filled with water, close the end of the tube near your lips by 
pressing between the thumb and finger. Now lower this end to a 
point lower than the level of the water in the vessel. Remove the 
pressure from the tube. Does the water flow through the tube? 
If not, try refilling the tube. Now carefully raise the. open end of 
the tube, noting the effect upon the rate of flow of water. Does 
the water continue to flow after the free end of the tube has been 
aised above the level of the surface of water? Such a piece of 
apparatus is called a siphon ; the water is said to have been re- 
oved from the vessel by siphoning. 



436 



WATER SUPPLY AND SEWAGE DISPOSAL 



514. Explanation of the Siphon. — In the experiment, the 
water in the long arm of the siphon fell through the tube. In 
so doing it tended to produce a vacuum in the upper portion, 
the bend, of the tube. Air pressure upon the surface of the 
water in the vessel forced the water up into the vacuum. 
This water then fell and more water was forced up into the 
bend. Thus the action continues till the level of the water 
falls below the open end of the tube in the vessel. How does 
the air vent provided in plumbing, then, prevent siphoning? 




Fig. 263.— The siphon flushing 
tank. A. When not flowing; B. 
When flowing. 

If a hole were made in the rubber tubing used in Ex. 81 at the 
top of the bend, would it destroy its siphoning action? 

515. The Siphon Flushing Tank. — The principle of the 
siphon is utilized in the ordinary flushing tank used in con- 
nection with water closets. Figure 263 shows the construc- 
tion of such a flushing tank. The trap consists of a hollow 
cast-iron cylinder about 3 in. in diameter and 12 in. in length. 
A vertical partition extending nearly the entire length of the 
trap divides its interior into two chambers, or rather into two 



DISPOSAL OF SEWAGE 437 

passages. One side of the trap, near its base, is so cut away 
as to produce an opening into one of the two passages at that 
point; the other passage opens downward directly into the 
discharge pipe. The lower end of the trap fits tightly upon 
a cushion so as to seal the passage into the discharge pipe 
when the trap is properly seated. When raised an inch or 
two, the trap permits the water to rush directly into the dis- 
charge pipe. If the trap be again dropped upon its seat, the 
discharge pipe, now filled with water, together with the two 
arms, or passages of the trap, becomes a perfect siphon. The 
discharge pipe and the right-hand passage in the trap form 
the long arm of the siphon and the left-hand passage forms the 
short arm. From our study of the siphon, it is evident that 
the water will continue to flow through the siphon thus formed 
till the water level sinks to the level of the opening in the side 
of the trap, air there enters and destroys the. siphoning 
action. The tank then again fills to the height permitted by 

the AUTOMATIC FLOAT VALVE. 

516. The Float Valve or Automatic Cut-off. — In many 
cases other than the flushing tank it is desirable to have the 
height of water in tanks automatically controlled. In such 
cases a float, as shown in Fig. 263, is frequently used to 
operate the cut-off valve. The float is a light, hollow, brass 
or copper sphere. When the water is lowered, the float falls, 
thus permitting the valve to open; as the water rises again, 
the float is forced upward until it closes the valve. 

V. DISPOSAL OF SEWAGE 

517. Disposal of City Sewage. — In cities having sewer 
systems the final disposal of sewage gives the individual citi- 
zen little or no worry. He merely connects his drain in 
proper manner with the city sewer; the city is responsible 
for the final disposal of the sewage. In many cases, city 
sewage is merely conveyed to, and emptied into, the nearest 
stream, always polluting it more or less, depending upon the 



438 



WATEK SUPPLY AND SEWAGE DISPOSAL 



amount and kind of sewage and the size of the stream. Our 
little friends, the ever-present bacteria, however, at once be- 
gin their work of decomposing the organic matter in the 
sewage and, under favorable conditions and with sufficient 
dilution, most of the polluting matter is soon destroyed and 
the stream again becomes reasonably clean and pure before 




Fig. 264. — Pollution of ground water: sewage discharging into sink- 
holes. 

its waters have proceeded far down stream. Sanitarians 
regard this as a primitive and unscientific method of dis- 
posing of sewage. This method of disposing of city sewage 
is now generally being abandoned and more scientific methods 
adopted. Most states in the east and central west now con- 



DISPOSAL OF SEWAGE 439 

trol stream pollution, through Boards of Health, proper dis- 
posal of sewage being required to suit conditions. 

518. Disposal of Sewage from Isolated Residences. — In 
the case of isolated buildings, such as farmhouses, country 
residences, and institutions, out of reach of city sewer sys- 
tems, provision must be made for the final disposition of 
sewage. In solving this problem, the laws and principles of 
science, as far as they are understood, must be observed at 
every step. Before this problem had been carefully studied 
many serious mistakes were made. 

519. The Leaching Cesspool. — Formerly the sewage from 
an isolated residence was often conveyed into a cesspool (see 
Fig. 244). Such a cesspool was merely a small, brick-walled, 
well-like receptacle a few feet in depth dug in the ground. 
No attempt was made to construct the cesspool water-tight. 
It was intended that the liquid portions of the sewage should 
soak, or leach, out into the surrounding soil. This, of course, 
polluted the soil, and, since the water table frequently rises to 
a point near the surface of the soil, the ground-water became 
contaminated. In fact, in cases where much water was sent 
into the cesspool, the sewage constantly found its way down 
into the ground-water, thus endangering all nearby wells 
(Fig. 264). If this same sewage had been spread thinly over 
the surface of the soil, or better still had been covered by a 
few inches of soil, it would quickly have been decomposed by 
bacteria and rendered harmless. Such bacteria are abundant 
only near the surface of the soil ; at the depth of the bottom of 
a cesspool they are not numerous, nor can they become numer- 
ous, therefore, the sewage which leached from the old-style 
cesspool into the ground-water was practically unaffected by 
the decomposing and purifying action of bacteria. Sanitary 
engineers, and students of sanitation generally, now agree that 
the cesspool is an unsanitary method of disposing of sewage. 
They are also agreed that one of the most feasible and sanitary 
methods of disposing of sewage in case of isolated residences 



440 WATER SUPPLY AND SEWAGE DISPOSAL 




tpcd, Ourier TO 
us Su/rrAtt 



Fig. 265. — A septic tank. (From Practical Up-To-Date Plumbing, 

Clow.) 











pV-SIod^e blowoff pipe 
Q*?)«--Valve 








; i 




F 

1 




z> 




u 

Septic Tank 




• 






• 









35=1 



■Plan 



Manhole 




sob soil ti'le 



Section 



Fig. 266. — Plan and section of septic tank suitable for medium 
sized residences, two compartments. (Courtesy of Chas. Brossman.) 



DISPOSAL OF SEWAGE 



441 



is by using some type of septic tank or disposal tank and 

SUBSURFACE DRAINS. 

520. The Septic Tank. — The modern septic tank consists 
of two, and often three, compartments (Figs. 265 and 266). 
Each of these compartments is cemented so as to be water- 
tight. The sewage from the house enters compartment No. 1. 
In this compartment anaerobic bacteria (Art. 318, page 287) 
attack the sewage and by decomposing it soon cause the solid 
material to dissolve, or, as we say, to liquefy. When work- 
ing properly, this process requires but a short time to liquefy 
most solid material in sewage. Even paper and cloth are 
liquefied within a few weeks or months. The liquefying 



Underdraws 



_ . Plan X 
Tank /"^ 



jL 



-/ 




~$*iltWR 



JEllevaiion 



^oroos^raveltor Sand 



\ 




Fig. 267. — Plan and section showing septic tank and subsoil filter. 
(Courtesy of Chas. Brossman.) 



action of these bacteria sets free considerable quantities of 
carbon dioxid, ammonia, and other gases which escape around 
the cover of the tank ; it also breaks all fats into small particles, 
which rise to the surface of the liquid and there form a tough, 
leathery scum which completely excludes the air, thus pro- 
ducing ideal conditions for the existence of anaerobic bacteria. 
To prevent the still undissolved solids from being stirred up 
by the in-rush of fresh sewage a partition, or baffle plate, 
is placed across the tank in front of the opening of the house 
drain. 
From compartment 1 (Fig. 265) the liquid sewage passes 



442 



WATER SUPPLY AND SEWAGE DISPOSAL 



into compartment 2. In this compartment the bacterial ac- 
tion still continues, but the chief purpose of the compartment 
is to serve as a storage tank. It is called the dosing tank. 
The sewage in this compartment should be fairly clear and 
nearly free from sediment, but still contains large amounts of 
undecomposed organic matter. The sewage accumulates in 
this compartment till it is nearly full and is then drawn off 
through the intermittent siphon in compartment 3 into the 
subsurface drains (Fig 267). Compartment 3 is sometimes 
omitted and the siphon is placed in compartment 2, the dosing 
tank, where it is submerged by the liquid (Fig. 266). It is 
more convenient, however, to set the siphon in a separate 
compartment, since it is necessary occasionally to examine 
the siphon to see that it is working properly. 

521. The Imhoff Septic Tank. — A septic tank of some- 
what more expensive construction is now generally used in 




Side View. 
Fig. 268.- 



End View. 
-Imhoff Tank. 



disposing of sewage from cities and institutions where con- 
siderable quantities must be taken care of. In the Imhoff 
type, the septic tank is really composed of two compart- 
ments, one suspended within the other (Figs. 268-9-270). 
The inner, suspended compartment is the settling chamber; 
the lower compartment is the sludge chamber. The two sides 
of the settling chamber do not quite meet at the bottom (Sec. 



DISPOSAL OF SEWAGE 



443 



ImboffTank 



HE 




Fig. 269. — Imhoff type of tank and sand filter for small institutions. 
(Indianapolis Country Club.) (Courtesy of Chas. Brossman.) 




Fig. 270. — Imhoff tank showing sludge formation at sides. Settling 
chamber in center. Dosing chamber in foreground. Sewer inlet shown 
at far end. (Julietta, Ind.) (Courtesy of Chas. Brossman.) 

AA, Fig. 269). As the sewage passes through this settling 
chamber, the solid matter settles through this opening into the 



444 WATER SUPPLY AND SEWAGE DISPOSAL 

sludge chamber below. It is chiefly in the sludge chamber 
that liquefaction or digestion takes place as a result of the 
action of the anaerobic bacteria. This type of septic tank 
is considered superior because the contents of the sludge 
chamber are but slightly disturbed by, or mixed with, the 
constant in-flow of fresh sewage. The bacterial action is, 
therefore, more certain and perfect. 

522. Sludge and Its Disposal. — Even when operating at 
its best, considerable insoluble material accumulates in the 
bottom of a septic tank. This accumulation is known as 
sludge. Occasionally the sludge must be removed from a 
septic tank. It is claimed that the Imhoff type of septic tank 
produces a sludge more solid and more readily handled than 




Fig. 271. — Contact niters of stone. (Julietta, Ind.) Sewage is dis- 
charged from tank, Fig. 270, to these beds. (Courtesy of Chas. Bross- 

man.) 

that produced by tanks of the type shown in Figs. 265 and 
266. Sludge from septic tanks is valuable as fertilizer. 

523. The Complete Oxidation of the Sewage. — In the 
septic tank only partial oxidation of the organic matter in the 
sewage ever takes place. "While the outflowing sewage from 



DISPOSAL OF SEWAGE 445 

the septic tank should be fairly clear and free from sediment, 
it still contains large amounts of undecomposed organic matter 
in solution. The methods followed and apparatus used to 
accomplish the final and complete oxidation of the sewage 
depends upon surrounding conditions and the amount of 
sewage to be handled. If small amounts of sewage only are 
to be disposed of, and the character of the soil permits, the 
final oxidation may be accomplished by means of subsoil 
drains and underdrains only (Fig. 267). If large amounts 
of sewage are to be disposed of, or if the surrounding soil 
is not reasonably open, porous soil, contact filter beds or 
sprinkling filter beds are generally provided (Figs. 269, 
271, 272 and 273). In either case the same general principles 
are applied ; namely, suitable conditions are provided whereby 
aerobic bacteria may work upon the sewage, completing its 
oxidation to mineral matter. 

524. The Subsurface Drain. — After passing through the 
siphon the sewage enters the subsurface drain (see Fig. 267) . 
This is merely a line of drain tile laid a few inches beneath 
the surface of the soil. The septic tank must evidently be 
constructed on higher land than the plot used for the drain- 
age. All joints between the tile are left slightly open, from 
14 to % in. To prevent dirt from entering through these 
open joints, a piece of a larger tile is laid over each joint. 
The liquid sewage readily passes out into the soil through these 
open joints. Here it is attacked by aerobic bacteria (Art 
318) and is completely decomposed, i.e., it is completely 
mineralized. 

Since aerobic bacteria live and multiply only in the presence 
of an abundance of air, they are to be found in large num- 
bers only near the surface of well-drained soil. It is be- 
cause the aerobic bacteria can not survive without an abundant 
supply of air that the intermittent siphon is used to empty 
the septic tank. If the discharge from the tank were constant 
and steady, the ground surrounding the upper end of the 



446 



WATER SUPPLY AND SEWAGE DISPOSAL 



drain would constantly be water-soaked, thus preventing air 
from entering the soil, and therefore preventing the sewage 
from being acted upon by aerobic bacteria By using the 
siphon, the contents of the tank are completely discharged 
into the drain once in from 6 to 24 hours, and the volume 
discharged, at one time, is sufficient to fill the drain its entire 
length. The area covered by the drain is intended to be 
great enough to insure the complete oxidation and minerali- 
zation of the sewage of one discharge before the next dis- 
charge occurs. 

525. The Contact Filter Bed. — "When the amount of sew- 
age to be handled is too great, or the character of the soil is 
such as not to permit of the successful use of the subsoil drain, 
contact beds or sprinkling filter beds are provided (Figs. 




Fig. 272. — Diagram of a Sprinkling Filter. 

269 to 273). Contact beds are merely beds of gravel, 
broken stone, or coarse sand. The sewage is run out from the 
dosing tank upon the surface of these beds. As it soaks down 
through the sand or gravel, the organic matter adheres to. or 
is deposited upon, the surface of the rock particles, where it 
is attacked and destroyed by aerobic bacteria. The sewage is 
retained in the contact bed for a fixed period of time and 
then is drawn off, thus permitting air to enter all spaces be- 
tween the rock particles, a necessary condition for the growth 
and multiplication of aerobic bacteria. The water drawn off 



DISPOSAL OF SEWAGE 



447 



from such a bed should be practically free from organic or 
other injurious matter. 

526. The Sprinkling Filter Bed. — A more effective and now 
generally used filter bed, is the sprinkling filter bed (Figs. 
272 and 273). In any filter bed the growth and rapid multi- 
plication of aerobic bacteria depends upon three factors: 
first, plenty of suitable food; second, plenty of oxygen; 
third, a moderate temperature. In the contact bed the first 
and third conditions are easily obtained. The second condi- 
tion, that of supplying the bacteria with plenty of oxygen is 
not so easily met. 

The sprinkling filter bed is now in general use because it 




Fig. 273. — Sprinkling filter in operation at Columbus, Ohio. 
(Courtesy of John Wiley & Sons.) 

provides for furnishing the sewage with a larger amount of 
oxygen. Instead of merely running the sewage over the bed 
and allowing it to soak into the bed, the sewage is under some 
8 or 10 feet of "head" i.e., the sewage in the dosing tank is 
8 or 10 ft. above the level of the sprinkler, and is allowed to 
pass through sprinklers which throws the sewage into the 
air in a fine spray just as a garden sprinkler throws a fine 



448 



WATER SUPPLY AND SEWAGE DISPOSAL 



spray of water upon the lawn. This fine spray of sewage 
absorbs oxygen from the air until it is saturated. 

527. The Activated Sludge Process.— The activated 
sludge process is a method of sewage disposal which is just 
coming into use if necessary. It is a still more rapid process 
of changing the organic matter in sewage to mineral matter 
through the action of aerobic bacteria. 

In the activated sludge process much less land is required 
for the plant. The original cost of the plant is less than it 
is when the Imhoff tank and either a contact filter or a 
sprinkling filter is used. It costs more to operate the plant, 
however. 







^— u 



.Fresh Sewage 



u aP 

SIudgel-pcL 
Pump I -t^~ 



Aeration Tank 

^■s Porous Plates in Bottom 



Aeration Tank 



I Effluent flows over top of the 



Fig. 274. — Diagram of an Activated Sludge Tank. Upper portion is 
cornering view in perspective; lower portion is the top plan. 

The activated sludge process is easily understood. The 
equipment consists of a concrete tank, often a hundred feet 
or more in length and perhaps 10 or 12 feet wide and about 8 
or 10 feet deep. In the bottom of this long tank porous plates 
are placed above a passage through which air is pumped. 



DISPOSAL OF SEWAGE 



449 



Fresh sewage, however, 
The name of this process, 
from the fact that about 



Fresh Sewage 



"1 



- Jf Sludge Pump 






Sludge, from 

Settling Tank 



Fig. 274A.— View of the left 
end of the activated sludge 
tank. 



The air passes up through the porous plates in very numerous 
and small bubbles which rise through the sewage. The sew- 
age, as it passes along through the tank appears to be boiling 
violently, on account of the bubbles of air coming up through 
it. Thus, we see, plenty of oxygen is furnished the bacteria 
in the sewage. 

does not contain many bacteria, 
'activated sludge process,' ' comes 
[ /s of the thick, chocolate-colored 
sludge which has settled at the 
bottom of the tank at the end 
farthest from end where the fresh 
sewage enters is pumped over 
into the first end of the tank and 
there mixed with the fresh sew- 
age. This sludge fairly swarms 
with aerobic bacteria. The pur- 
pose of pumping the sludge into the first end of the tank with 
the fresh sewage is to furnish plenty of bacteria to consume 
the organic matter which is in the fresh sewage, Fig. 274. 
528. Summary of Sewage Disposal. — The following points 
should be learned and remembered : 

First, Mother Nature has provided that bacteria shall live 
upon the dead bodies of plant and animal life, and upon the 
waste organic materials which are produced by animals and 
plants while still living. The dead bodies of plants and ani- 
mals and waste materials which are produced by plants and 
animals while living are the natural food materials for a vast 
number of bacteria. 

Second, There are many different kinds of bacteria which 
thus live upon the waste materials of plant and animal life. 
Some of the forms of bacteria live and develop only in the 
absence of oxygen. These kinds are called anaerobic bac- 
teria. Most, if not all, offensive odors resulting from the 
"decay of organic matter" are produced by the activities of 



450 WATER SUPPLY AND SEWAGE DISPOSAL 

these anaerobic bacteria. Few, if any, offensive odors, are 
produced by the activities of aerobic bacteria. 

Third, Generally the activities of anaerobic bacteria do 
not result in the complete changing of organic wastes into 
mineral matter which becomes food for plant life. Only a 
portion of such organic wastes are changed into mineral mat- 
ter by anaerobic bacteria. 

Fourth, If the wastes from plant and animal life are 
spread thinly upon the soil, or slightly covered by soil, aerobic 
bacteria quickly changes them into mineral matter, few, if any, 
offensive odors resulting. 

If, however, the organic waste matter is found in large 
masses, such as the dead bodies of animals or large accumula- 
tions of other wastes, anaerobic bacteria first attacks the mat- 
ter. The results are these: Some of the organic matter is 
decomposed into mineral matter but the principal effect is the 
breaking apart of the matter so that oxygen can enter and 
make it possible for aerobic bacteria to live and feed upon the 
waste material. While the anaerobic bacteria are working 
offensive odors are given off. 

Fifth, Every successful attempt to dispose of sewage has 
been an application of these facts. 

Sixth, The term "sewage" is applied to waste matter, 
much of which comes from animal and plant life, which is 
disposed of by being washed into underground sewers by 
means of water. 

Seventh, All waste matter resulting from plant or animal 
life may be disposed of by the following methods : 

(1) While comparatively dry it may be spread upon the 
surface of the soil or slightly covered. 

(2) If a stream of water is available in which a sufficiently 
large amount of water is flowing, such wastes may be placed 
in the stream without greatly polluting it. Sewage run into 
such a stream is said to have been disposed of "by dilution." 

(3) If suitable soil in suitable areas is available, sewage 
may be disposed of by applying the sewage to the surface or 



DISPOSAL OF SEWAGE 451 

near the surface of the soil at suitable intervals, i.e., at such 
intervals as will permit the aerobic bacteria to decompose each 
dose before the next dose is applied. Such a method is called 

" BROAD IRRIGATION BY SEWAGE." 

(4) An Imhoff tank and contact filter bed may be used 
where little land is available or where the land is not suitable 
for broad irrigation. 

(5) The sprinkling filter bed is regarded as more reliable 
and satisfactory than the contact filter bed and has generally 
replaced it. The oxygen supply is more reliable than in the 
contact bed. 

(6) The activated sludge method of sewage disposal has 
lately come into use and is regarded by many sanitary en- 
gineers as the best method of sewage disposal. Theoretically 
it is the ideal method of sewage disposal because the fresh 
sewage is thoroughly seeded with aerobic bacteria and the 
mixture is thoroughly saturated with oxygen. 



CHAPTER XI 
MACHINES, WORK, AND ENERGY 

I. MACHINERY IN THE HOME AND ON THE FARM 

529. The Tools of the Early Colonist and Pioneer. — In 

early colonial days practically all work was done by hand. 
When machines were used they were of the simplest kind. 
This has always been the case with pioneers. When the col- 
onist or pioneer wished to build a new home, he supplied 
himself with a rifle, a knife, and an ax, a hatchet, and a saw 
and went forth into the woods. With his rifle and knife he 
supplied himself with food. With his ax he felled the trees 
and constructed his log house. He made all his own furni- 
ture — his chairs, his table and his bedstead. He fashioned 
out of wood such other conveniences as he needed. 

530. Agricultural Tools of the Colonist and Pioneer. — 
When the pioneer had ''cleared' 7 a small space around his 
cabin, he naturally wished to raise some grain and garden 
truck. At first, the land was generally very fertile and free 
from weeds; little cultivation was necessary. In the spring 
the seed was scratched into the soil. In the fall the crop was 
harvested by using such tools as the pioneer could make. The 
corn was shelled and the wheat threshed by hand. The 
corn and wheat were ground into meal and flour between 
stones. 

Later, as the pioneer's efforts at agriculture became more 
varied and he had oxen to help him, he secured a cast-iron I 
plow. He also secured a hand sickle and finally a cradle to aid 
him in harvesting his grain. He likewise made a flail for 
threshing it. As settlers became more numerous, grist mills 
were built upon the streams, and settlers from far and nearl 
carried their grain to these mills to be ground into meal and 
flour. Even then, their agricultural tools were so few and so| 

452 



MACHINERY IN THE HOME AND ON THE FARM 453 

poorly adapted to their needs that the farmer of today, were 
he obliged to use them, would feel helpless. 

531. Household Tools of the Colonist and Pioneer. — The 
kitchen equipment and dishes of the pioneers were few indeed. 
A kettle or two, a few plates, and some knives and spoons 
constituted their cooking and serving equipment. But very 
early they found use for other household tools. It was im- 
possible for them to buy clothing, therefore, they soon began 
to raise flax and wool in the northern colonies and cotton in 
the southern colonies and to make their own clothing. To do 
this they were obliged to make tools for carding, spinning, 
and weaving of "homespun" cloth. While these tools were 
crude and simple, they answered the purpose for which they 
were intended, and every member of the household became 
skilful in using them. 

532. Pioneers were Skilful in the Use 'of Tools. — Al- 
though the colonists and pioneers had few tools to use, they 
were far more skilful in the use of such tools as they did have 
than are most of us to-day. There were no factories to manu- 
facture the many articles they needed for their comfort, nor 
did they have money with which to buy them. We can, per- 
haps, appreciate the skill of the colonists in the use of tools 
when we realize that they not only sheared the sheep, cleaned, 
washed, picked, carded, spun, dyed, and wove the wool into 
cloth and made the cloth into clothing, but were also obliged 
to make practically all the utensils used in these processes. 

533. The Coming of the Factory. — About the beginning of 
the 19th century (1800) improved machinery, driven by water 
power, began to be used in the making of cloth. It was soon 
found to be more economical to buy cloth made in the factory 
than to make it in the home. During the 19th century, cotton 
and woolen mills with power-driven machinery were developed. 
At the present time no one thinks of manufacturing cloth in 
the home. Today much of the cloth is made up into garments 
ready to wear before leaving the factory. 

The 19th century was a period where there were few 



454 MACHINES, WORK, AND ENERGY 

machines and labor-saving devices in the home. All this 
means that knowledge concerning machines and machinery 
largely disappeared from the home. 

534. Knowledge of Machinery again Becoming Necessary 
in the Home., — While almost all the primitive industries have 
disappeared from the home, there have recently come into the 
home many new forms of machines and devices all of which 
make necessary some knowledge of applied science. Lighting 
systems of various kinds, heating devices, systems of water 
supply, plumbing, vacuum cleaners, sewing machines, washing 
machines, cream separators, and motors for the operating of 







Fig. 275. — A farm power house. 

machinery of various kinds — all these conveniences require 
knowledge of applied science. The housewife with no knowl- 
edge of the laws of science can not expect to handle success- 
fully the conveniences of the modern home. 

535. Knowledge of Mechanics Necessary for the Farmer. 
— Today the farmer requires a knowledge of mechanics at 
every turn. Most of the work on the farm is now done by 
means of machinery. The farmer with no knowledge of the 
laws of mechanics can not operate intelligently his plows, cul- 



SOME COMMON MACHINES 455 

tivators, mowing machines, binders, seeders, or numerous other 
tools found upon every farm. Moreover, many farms are now 
supplied with a power house in which a gasoline engine fur- 
nishes the power which runs the pump, cream separator, 
churn, corn sheller, feed grinder, and possibly a dynamo for 
generating the current for electric lighting and a circular 
saw for sawing wood (Fig. 275). Many farmers now own 
automobiles, and these machines require a good knowledge of 
mechanics if they are to be handled with safety and economy. 
If all auto drivers were familiar with the laws of mechanics, 
many accidents would be avoided. 

536. This, an Age of Machinery. — The farmer and the 
housewife need to learn a lesson from the factory and the 
well-organized industrial plant. There, one man often op- 
erates a machine which does the work formerly requiring the 
labor of 10, 100, or possibly 1000 men. Rapidly the farmer is 
learning to avail himself of the advantages of using machin- 
ery. As yet, the housewife has made too little use of machin- 
ery to aid her in her household duties. The cleaning of the 
house, washing and ironing, skimming of the milk and churn- 
ing of the butter — these and many other processes are carried 
on by hand with little thought of using easily obtained labor- 
saving devices. 

Make a list of the labor-saving machines for use on the 
farm and in the home. 

II. SOME COMMON MACHINES 
The Sewing Machine 

537. Earliest Sewing Machines. — The first sewing machine 
of which there is authoritative record was invented by an 
Englishman, Thomas Saint, in 1790. It was not known that 
he made more than one machine. This machine, as well as 
others made during the following 50 years, was intended for 
embroidery and fancywork, not for practical purposes, such 



456 



MACHINES, WORK, AND ENERGY 



as the making of garments or other useful articles. All of the 
earlier machines were run by hand and were awkward, clumsy 
affairs constructed chiefly of wood 
and having many serious defects. 
The sewing machine did not seri- 
ously affect American life until 
after the middle of the 19th cen- 
tury. About 1850 really practi- 
cal machines were invented. 
Even these machines were crude 
compared with the machines of 
today (Fig. 276). 

538. Classes of Sewing Ma- 
chines. — Sewing machines may 
be classified according to the kind 
of stitch they make. Although 
a great variety of stitches have 
been used at different times — 
some 75 in number — practically 
only three kinds of stitches are 
today in use. They are the lock 

stitch, the chain stitch, and the buttonhole stitch. The 
lock stitch is the most common and, for most purposes, the 
most satisfactory. Chain stitch machines, however, have ad- 
vantages for certain purposes: 




Fig. 276. — Sewing machine, 
L850. The shipping box was 
used as a table for the ma- 
chine. 



Exercise 82. — A Study of the Chain-stitch Seam and the Lock- 
stitch Seam 

Secure samples of the chain-stitch seam and the lock-stitch seam, 
each sewed in loosely woven cloth cut on the bias. First, examine 
each seam to see which is more elastic, and second, note the ease 
with which each seam may be ripped. Can you rip out the entire 
chain-stitch seam by merely breaking one stitch and pulling upon 
the broken thread? Can the lock stitch seam be ripped in this 
manner? 



1. Chain-stitch machines are simpler in construction and 
generally use but a single thread. 2. The thread, when 



SOME COMMON MACHINES 



457 



sewed into a seam, is readily removed, i.e., the seam is quickly 
ripped out by the mere breaking of the thread. 3. The seam 




presser. nor 



HEEL OF LOOPS* 



PRESSER FOOT 




PRESSER FOOT 



POINT Qf LQOPER 




HE.CL OF LOQPEI 



POINT OF LOOPER 



Fig. 277. — How a chain-stitch machine forms the knot, 

sewed by means of the chain stitch is elastic, while the lock- 
stitch seam is not. 4. The chain-stitch machine can be oper- 
ated satisfactorily at a higher speed than the lock-stitch 



458 



MACHINES, WORK, AND ENERGY 




P^ESSCR foot 



POINT OF SHUTTLE 



BOBBIN OF 
UNOEf\ THREAD 




1. Point of shuttle entering loop of 
needle thread. 



2. Shuttle in loop of needle 
thread. 




BOBBIN OP 

UNDEf? TW.tm 



4. Stitch completed. 
Fig. 278. — How a vibrating-shuttle machine forms the knot. 



3. Shuttle thread enclosed by needle 
thread. 



machine. Figure 277 shows the manner in which the chain- 
stitch machine forms the stitch. 



SOME COIDIOX MACHINES 



459 



Chain-stitch machines are frequently used in factories pro- 
ducing ready-made garments on account of their greater 



TWEJiOOlUW 




L Hook entering the loop of the needle 
thread. 



BOBBIN CASE 
ROTATING HOQJ\ 



2. Loop of needle thread en- 
closing bobbin case. 



Fig. 279. — How a rotary hook makes the knot. 



speed. Owing to the ease with which a chain-stitch seam may 
be ripped, and the liability of a stitch's being broken by ac- 



460 



MACHINES, WORK, AND ENERGY 



cident, the chain-stitch seam is not regarded as satisfactory 
for many purposes. 




H0TATIN0 H00H 



3. Under thread enclosed by needle thread. 4. Stitch completed. 
Fig. 280. — How a rotary hook makes the knot. 

539. Classes of Lock-stitch Machines. — Lock-stitch ma- 
chines are classified according' to the way in which the stitch 
is formed. The common classes are rotary-hook, oscillat- 



SOME COMMON MACHINES 



461 



ing-hook or oscillating-shuttle machines, and vibrating- 
shuttle machines. 

While the majority of all lock-stitch machines in use today 
are of the vibrating-shuttle type (Fig. 278), certain rotary- 
hook machines have been among the most successful from the 
first. In 1851, Mr. A. B. Wilson invented a rotary-hook 
machine, the first of that type, which was very successful. 
Figures 279 and 280 show the way in which the rotary-hook 
machine forms the stitch. 

In the rotary-hook machines, the hook makes one complete 
rotation for each stitch. 




Fig. 281. — Head of a vibrating-shuttle machine. 

In the oscillating-hook or oscillating-shuttle machine, the 
hook or shuttle makes one-half of a rotation, i.e., turns one- 
half way around on its axis, and then reverses and returns to 
its former position, for each stitch. 

In the vibrating-shuttle machine the shuttle may move in a 
straight line or in the arc of a circle. In either case, the 
shuttle makes one complete vibration, i.e., a motion forward 
and back, for each stitch. 



Exercise 83. — A Study of the Sewing Machine 

(This exercise may be studied at home if no machine is available 
at school.) 



462 



MACHINES, WORK, AND ENERGY 



1. Note the name of the machine. 

2. Note just how the motion of the -treadle is transferred to the 
drive wheel by means of the pitman. One complete vibration of 
the treadle produces how many revolutions of the drive wheel? 

3. Measure the diameter of the drive wheel. What, then, is its 
circumference? Measure the diameter of the pulley on the head of 
the machine over which the belt passes. What is its circumference? 

4. Provided there is no slipping of the belt, how many revolutions 
of the pulley will be produced by one revolution of the drive wheel? 

5. The top of the balance wheel -moves from you when the machine 
is running in the right direction on some machines. On other ma- 
chines the balance wheel turns in the opposite direction, i.e., the 
top of the wheel moves towards you. It is always best to discover 




Fig. 282. — Head of a rotary-hook machine. 

the proper direction in which to turn the balance wheel before at- 
tempting to sew. Turning the wheel in the wrong direction is 
likely to break the thread. 

By watching the movement of the feeder beneath the presser 
foot can you tell which is the proper direction in which to turn the 
balance wheel in starting the machine? If possible, find out the 
proper direction on several different kinds of machines. 

6. Turn the pulley carefully and see how many stitches are taken 
by the needle for each revolution of the pulley. How many stitches 
are taken, then, to each complete vibration of the treadle? Move 
the treadle through one complete vibration and count the number of 
stitches taken to check your calculation. 

7. Place a piece of cloth in position and stitch a seam for 10 
seconds by the watch. Let one assistant watch the time while a 



SOME COMMON MACHINES 463 

second assistant counts the number of vibrations of the treadle. 
How many stitches, then, are taken per minute? (Some manu- 
facturers claim that as many as 3000 stitches per minute have been 
taken with their machines.) 

8. Remove the face plate, if removable, and discover exactly how 
the rotary motion of the pulley is changed to a vibratory motion of 
the needle and the take-up lever. 

9. Note exactly how the presser-foot is raised from the cloth. 
What is its purpose? 

10. Examine the feeding device and determine how it works. 
Just how is the length of the stitch regulated? Does the length of 
the stitch depend upon the speed with which the needle acts or 
upon the motion of the feeder? Be certain that you understand 
the regulation of the length of the stitch. 

11. Is the machine studied a chain-stitch or a lock-stitch machine? 
Note exactly how the stitch is made. 

12. If the machine is a lock-stitch machine, determine whether it 
is (a) a rotary-hook machine, (b) an oscillating-hook or oscillating- 
shuttle machine, (c) or a vibrating-shuttle machine. 

13. Determine exactly how the knot is produced. Does the loop 
which forms the knot pass completely around the hook or shuttle? 
If so, describe exactly how it does so. Can the hook or shuttle, 
then, be rigidly attached to any fixed or moving part of the ma- 
chine? Do not decide this point till you have made a careful 
study of the way in which the knot is produced. 

The Cream Separator 

540. Importance of the Cream Separator. — The cream sep- 
arator is found nowadays in almost every creamery, in every 
city milk-supply house, in many dairies, and on most farms 
where any considerable quantity of milk is produced. It is 
one of the most common and useful machines. As its name 
implies, it is a machine used to separate the cream from the 
other portions of whole milk. 

541. Former Methods of Separating Cream. — Primitive 
man doubtless separated cream from the other portions of 
milk from the time he first began to use as food the milk from 
his herd of goats. Until recent times the separation was 
usually made by placing the milk in shallow crocks, jars, or 
pans. The cream, being lighter than the other portions of 



464 MACHINES, WORK, AND ENERGY 

the milk, rose to the top and could then be removed, leaving 
the skim milk undisturbed. Frequently the skimming was 
not made until the milk had become sour, thus giving the 
cream as much time as possible to separate. This method is 
known as the shallow setting method. 

Several years ago the deep setting method largely dis- 
placed the shallow setting method in the better dairies. In 
the deep setting method, the milk is placed in deep cans 
which are usually placed in vats of cool water. By thus keep- 
ing the milk at a low temperature, souring is delayed and, 
consequently most of the cream has time to become separated 
while the milk is still sweet and of greater use as food for 
man and his domesticated animals. 

A third method of cream separation is sometimes em- 
ployed. It is known as the water dilution method. If fresh 
milk is diluted by the addition of cold water (about half and 
half) the cream separates much more rapidly. This method 
is not often used because the separation of cream is not gen- 
erally so complete as in the case of the other methods, and 
because the skim milk is so diluted that it is less valuable. 

542. Principle of the Cream Separation. — In each of the 
three methods of cream separation given, the difference in 
weight, or more correctly stated, the difference in density of 
the cream and the skim milk is utilized to cause the separa- 
tion. It is much as if we were to fill a peck measure with a 
mixture of buck shot and peas and were then to shake the 
measure. The lead shot, being heavier than the peas, 
would settle to the bottom of the measure and the peas would 
be forced to the top. 

If, however, we were to fasten the measure securely to a 
rapidly rotating platform, the contents of the measure would 
fly out against the sides of the measure. The shot being 
heavier, or more dense, than the peas, would be forced 
more strongly against the outside of the measure. The shot 
would therefore be found to gather against the outside of the 
measure while the peas would form a sort of lining on the 



SOME COMMON MACHINES 



465 



inside of the shot. The force which holds the shot and peas 
away from the center of the measure is called centrifugal, 
force (centri, center and fugal, to fly from). 

The shallow setting, the deep setting, and the water dilu- 
lution methods of separating cream all depend upon the force 
of gravity to cause the separation and are therefore called 
gravity methods. With the cream separator, however, cen- 
trifugal force is employed to cause the cream and skim milk to 
separate. 




TWISTED 

ROPE 




X-ray view. Cen- 
trifugal force holds 
water against side 
of pail. 



Fig. 283. 



-The cream separa- 
tor. 



Exercise 84. — To Illustrate and Study Centrifugal Force 



1. Suspend from the ceiling by means of a braided cord (such 
as a small window-sash cord) a 12-qt. pail or bucket. Place about 
2 qt. of water in the pail. Seizing the bail of the pail, cause it to 
rotate rapidly (see X-ray of pail above). Watch the effect upon the 
surface of the water. When the motion dies down, give it another 
w^hirl in the same direction. Continue thus to whirl the pail till the 
braided cord has acquired considerable twist. Now, by placing the 
hand in the water, bring it to rest, at the same time preventing the» 



(466 



MACHINES, WORK, AND ENERGY 



cord from untwisting till the water is quiet. Now, let the cord un- 
twist ; it will cause the pail to rotate rapidly. Watch the effect upon 
the water in the pail. The shape which the water assumes will be 
more evident if numerous small fragments of paper or some saw 
dust be placed in the water. 

2. Place some water in a small pail and then swing the pail 
rapidly in a vertical circle over your head. Can you do so with- 
out allowing any of the water to fall out of the pail? Does this 
show that the centrifugal force may be greater than the force of 
gravity ? Explain. 



SWM-MILK OUTLET 



OUTLET 

IM-M1LK OUTLET 





Fig. 284. — Showing the construction 
and operation of the cream separator. 



Fig. 285. — The gearing of 
the cream separator. 



543. The Cream Separator. — In a cream separator (Fig. 
283) the heavier portions of whole milk, which constitute 
the skim milk, are separated from the lighter portions, which 
constitute the cream, by centrifugal force. In the type here 
illustrated, the whole milk is fed slowly down through the 
top opening 1 (Fig. 284). This tubular shaft is closed at 
its lower end but it has vertical slots in its lateral wings, 2 
and 2. Through these vertical slots the milk passes in thin 
sheets between rapidly revolving disks, 4 and 4, each of which 
is shaped somewhat like an inverted funnel. In the illustra- 



SOME COMMON MACHINES 467 

tion the space between the upper disks is greatly exaggerated 
for the sake of clearness. This disks revolve at a rate of from 
5000 to 10,000 r.p.m. (revolutions per minute). Figure 285 
shows the gearing by means of which this high rate motion is 
obtained. 

The resulting centrifugal force is very great. The heavier, 
i.e., denser, portion of the milk in each of the thin sheets is 
thrown outward or against the under side of the disk above, 
while the cream being lighter, i.e., less dense, remains against 
the upper side of the disk just below. Thus it is that the 
cream is separated from the skim milk. The cream accumu- 
lates at the center of the separator as shown by the lighter 
shading, 3, 3, in the illustration (Fig. 284), while the heavier 
skim milk is forced to the outside of the separator and finally 
past the lower rim of the disks as shown by the darker shad- 
ings in the illustration. It will be noted that the wings, 2 
and 2, through which the whole milk passes, extend past the 
rising column of cream, thus avoiding any remixing of the 
cream with the milk. Since the fresh supply of whole milk is 
constantly flowing into the separator down the tubular shaft, 
it forces the separated cream upward and out at the cream 
outlet as shown by the dark arrows on the light background, 
and it also forces the separated skim milk upward and out at 
the skim-milk outlet as shown by the light arrows on the 
dark background. 

544. Advantages of the Cream Separator. — The advan- 
tages of using a cream separator are many : 1. The separation 
is more complete than by other methods. 2. The separation 
is best made while the milk is still warm, making it unneces- 
sary to cool and store large quantities of milk. 3. The skim 
milk is more valuable for feeding purposes when thus ob- 
tained while still fresh. 4. The cream obtained can be 
"ripened" more evenly (see Art. 397), thus pro- 
ducing butter of better quality and flavor. 5. In most states 
and cities whole milk offered for sale as food must contain a 
certain percentage of butter fat (Art. 395). Practically all 



468 MACHINES, WORK, AND ENERGY 

of the butter fat is contained in the separated cream. It is 
common practice in many states for milk dealers to separate 
the cream from the skim milk in the milk they handle. By 
then mixing the cream and skim milk in certain definite pro- 
portions they can produce milk containing an unvarying 
amount of butter fat. 1 6. It is common practice for farmers 
to separate the cream from the skim milk, shipping the cream 
to the creamery where it is made into butter and feeding the 
skim milk on the farm, thus saving much cost for transpor- 
tation. 

III. MASS, WEIGHT, FORCE, WORK, AND POWER 

545. Meaning of Terms. — In all study and use of machines 
we need to understand exactly the meaning of certain terms. 
No two people can talk intelligently about machinery and its 
operation unless both use the same terms to express exactly 
the same thought ; moreover, we must gain much of our knowl- 
edge concerning machinery from reading and it is impossible 
for us to understand what we read unless we know the exact 
meaning of the terms used. The terms used in all text-books, 
in reliable magazines, in all government reports, and in most 
advertising circulars, are carefully chosen and have certain 
definite meanings. If we are to be intelligent people and are 
to speak accurately when referring to mechanical matters, 
we must know the exact meaning of the terms we use. 

546. Mass. — By mass we mean the quantity of matter in an 
object. We never mean its weight, its size, or its density. 
When we buy a certain quantity of flour, sugar, eggs, bananas, 
potatoes, or coal, we are paying for a certain mass of the 
article purchased. We may determine and speak of the mass 
purchased in several ways: We generally speak of buying a 
certain number of pounds of sugar, or a certain number of 
eggs or bananas, or a certain number of pecks or bushels of 
apples. In every case, however, what we endeavor to do is to 
determine the mass of the article purchased. It is becoming 

1 This practice is prohibited by law in some states. 



MASS, WEIGHT, FORCE, WORK, AND POWER 469 

more and more common for all such commodities to be bought 
and sold by the pound-mass. A dozen bananas is an indef- 
inite quantity; likewise, a dozen eggs does not indicate clearly 
the amount of mass because they vary so greatly in mass. 
Some cities, states, and national governments have passed 
laws obliging all dealers to buy and sell by the mass instead 
of the dozen, or the peck, or the bushel. Nearly all com- 
modities are thus bought and sold when handled in large 
quantities. For example, while we speak of buying oats or 
corn at a certain price per bushel, we actually pay the price 
for 32 lb .-mass of oats or for 56 lb. -mass of corn. TVe shall 
see soon that we generally determine the mass by first deter- 
mining the weight, but we must never confuse the weight 
of an object with its mass. 

547. The Units of Mass. — The common unit of mass used 
in the United States is the pound. Originally the old English 
pound-mass was the mass of 7680 grains of wheat. During 
the reign of Henry VIII (1509 to 1547) the standard pound 
was reduced somewhat till it represented the mass of 7000 
grains of wheat, hence we say there are 7000 grains in 1 lb. 
The English government, many years ago, prepared a piece of 
platinum equaling this mass and declared that to be the 
standard pound. Since colonial days we have always ac- 
cepted this mass as the mass of a standard pound. 

Two other standard units of mass are the gram and the 
kilogram of the metric system. The metric" system of weights 
and measures is now used by all civilized nations except 
Great Britain and the United States. The gram-mass is the 
mass in 1 c.c. of water at 4°C. The kilogram equals 1000 
grams. In 1893 the United States government defined the 
avoirdupois pound as equal to 453.6 grams. The kilogram 
is, then, equal to as many pounds as 453.6 is contained times 
in 1000, or approximately 2.2. If the metric system of 
weights and measures is ever generally used in the United 
States, as it is now used in most of Europe, we shall buy 
butter and sugar by the kilogram instead of the pound. 



470 MACHINES, WORK, AND ENERGY 

548. Weight, Gravitation and Gravity. — By the weight 
of an object we mean the pull of the earth upon that object. 
We all know that any object which is free to fall does fall 
toward the earth. This is because both earth and object 
attract each other. Physicists and astronomers have proved 
that every body in the universe attracts every other body. 
In general, this attraction of bodies for other bodies is called 
the force of gravitation. When, however, we are speaking 
of the attraction between the earth and any object near its 
surface we speak of the force as the, pull of gravity. 

Now, if we support a body so that it is not free to fall 
towards the earth, it then exerts a push or a pull upon the 
support. It is this push or pull which we call the weight of 
the object. The weight of an object, then, is merely the meas- 
ure of the force of gravity upon it. We shall see later that 
weight is merely one form of force. It is now very evident 
that we do not go to the grocery to purchase a certain weight 
of sugar or to the meat market to buy a certain weight of 
meat. What we do wish to buy is a certain mass of sugar 
or mass of meat. 

549. How Weights and Masses are Determined. — The 
easiest way to determine the mass of an object, however, is 
to determine its weight. A 1-lb. mass has just 1 lb. of weight. 
Knowing this, we see that determining the weight of an 
object tells us at once its mass. This is not at all new to us 
when we stop to think of it. We have been used all our lives 
to seeing masses determined by determining the weights of 
those objects. We want to purchase a certain mass of meat ; 
the dealer determines the mass by determining the weight 
of the meat. While it is possible to determine the mass of 
an object without determining its weight at all, ordinary 
scales and balances simply tell us the weight of the object 
and it is because we accept the fact that a pound-mass weighs 
just 1 lb. that we are willing to accept this method of deter- 
mining the mass of our purchases. 

550. Beam Balances.— The most common, as well as the 



MASS, WEIGHT, FORCE, WORK, AND POWER 471 

most accurate, devices for determining the weights of objects 
are the various forms of beam balances. A beam balance 
consists of a rigid beam mounted horizontally upon a sharp, 
hard support called a knife-edge or fulcrum (Fig. 286). 
Each end of this beam carries a pan which is also suspended 
from a "knife-edge." Great care is taken to eliminate fric- 
tion. If the two arms of the balance are of exactly equal 
lengths, a 1-lb. mass upon one scale pan will axactly balance 
a 1-lb. mass upon the other pan. If the two arms of the beam 
balance be of unequal lengths, in order to balance each other, 
the two masses must be inversely proportioned to the lengths 
of the arms. A common example of a beam balance with 




Fig. 286. — Beam balance. 

unequal arms is the old-fashioned steelyards (Fig. 287). If 
in such a balance, the object whose weight is to be determined 
is 2 in. from the point of support while the known mass is 20 
in. from the support, then the weight of the unknown object 
is exactly 10 times that of the known mass. 

The weight of the known mass : the weight of the unknown 
mass : : 2 : 20. 

The weights are inversely proportioned to the lengths of 
the arms. 

Generally, scales used in weighing heavy objects are con- 
structed by using several such beams in combination. The 
common wagon scales are a familiar example of such a com- 
bination of unequal armed beam balances (Fig. 288). In 



472 



MACHINES, WORK, AND ENERGY 



such cases, it is common for the beams to be so combined that 
a 1-lb. mass will balance, perhaps, 1000 lb. or more. 




Fig. 287. — Common steelyards. 



Fig. 288. — Wagon scales. 



551. Spring Balances. — The principle of the spring bal- 
ance is very different. A coiled steel spring is 
mounted within a metal case (Fig. 289). The 
upper end of this coiled spring is secured to the 
upper end of the case; the lower end of the 
spring is free but carries a small rod or wire 
which, in turn, carries the hook upon which the 
mass whose weight is to be determined is hung. 

feE - i A small pointer, or index, fastened to the lower 

- end of the spring is so mounted that it hangs 

just in front of the face of the case, upon which 
is stamped the scale. When a mass is suspended 
on the hook, the coiled spring is stretched and 
the index indicates the weight. 

Spring balances are very convenient and easy 
to handle but usually they are not very accur- 
ate. Even though a spring balance may be care- 
fully made and fairly accurate when new, it is 
likely to wear with use and give false readings 





Fig. 289. 
— S p r i n g 
balances. 



later. 



MASS, WEIGHT, FORCE, WORK, AND POWER 473 

552. Force. — By force we mean a push or a putt. It is 
force which tends to produce motion in a body or to change 
the direction or speed of a moving body. All forces are 
pushes or pulls. Solids may be either pushed or pulled; 
liquids and gases, however, must be moved by being pushed. 
A railroad train may be either pushed or pulled; but water 
and air can be moved only by being pushed. Explain why 
this is so (see suction, Art. 284) . 

553. The Units of Force. — The names given to the units 
of force are the same as those given to the units of mass. 
We speak of a pound of force and a pound of mass; of a 
gram of force and a gram of mass ; of a kilogram of force 
and a kilogram of mass. This use of the same names for 
units of mass and units of force is unfortunate and confusing. 
Many people do not clearly see the difference between a pound 
of force and a pound of mass. We must never forget that a 
pound of mass is a certain quantity of matter while a pound 
of force is a certain amount of push or pull. We can eat a 
pound-mass of beefsteak but we exert a pound of effort when 
we lift the steak against the pull of gravity. 

554. Comparison of Force and Weight. — A pound of force 
is equal to the weight of a 1-lb. mass ; the gram-force is equal 
to the weight of a 1-gram mass; the kilogram-force is equal 
to the weight of a 1-kg. mass. It must be remembered, how- 
ever, that while weight always acts in a vertical line, i.e., 
toward the center of the earth, forces may act in any direction 
whatever. A team of horses pulling a plow exerts a force, 
but the direction of the force is in a nearly horizontal line. 
A locomotive usually exerts a pull, i.e., a force, which is almost 
exactly horizontal. A boy may throw a ball in any direction 
he chooses, but in doing so he exerts a force upon it. "Weight, 
then, is a term which we apply to a force due to a certain cause 
— the pull of the earth — and is always acting in a vertical line. 
Before we go further in this study of machinery we should 
be certain that we clearly understand the difference be- 
tween : 



474 MACHINES, WORK, AND ENERGY 

A pound-mass, a pound-weight, and a pound-force; 

A gram-mass, a gram-weight, and a gram-force; 

A kilogram-mass, a kilogram-weight, and a kilogram-force. 

555. Work. — By work we mean a push or a pull acting 
through distance. The table or desk which supports your 
books does no work. The columns which support the porch 
roof do no work. A man attempting to lift a piano which he 
is unable to lift, or a team of horses attempting to pull a 
loaded wagon which it is unable to move, does no work. As 
the term work is used in mechanics, no person or machine 
does work unless a force actually acts through space. A force 
exerted in an attempt to move an object which does not move 
is wasted effort — but no work is done. 

This use of the term work is not peculiar to mechanics ; it is 
really the common, everyday meaning of the term. When a 
man lets the contract for the building of a house, he agrees to- 
pay for the work done, never for effort put forth. The con- 
tractor, in turn, pays his man for the work they actually do. 
Even though the employer pays his men by the day, he con- 
tinues to employ only those who actually accomplish the re- 
quired amount of work. 

556. The Units of Work. — The common English unit of 
work is the foot-pound. The foot-pound is the amount of 
work done by a force of one pound acting through a distance 
of one foot. Since a 1-lb. mass weighs 1 lb., we do 1 ft.-lb. of 
work when we lift the 1-lb. mass 1 ft. against the pull of 
gravity; we also do 1 ft.-lb. of work when we support it so 
as to prevent it from falling while we lower it 1 ft. We do 
1 ft.-lb. of work whenever we exert a 1-lb. push or pull and 
succeed in moving the object pushed or pulled through one 
foot of distance. The direction in which the push or pull acts 
makes no difference if it is measured in the direction the 
object moves. We do work when we climb a flight of stairs ; 
we also do the same amount of work when we descend the same 
flight of stairs. 



MASS, WEIGHT, FORCE, WORK, AXD POWER 475 

The most common metric unit of work is the kilogram- 
meter. It is the amount of work done when a force of one 
kilogram acts through a distance of one meter. 

PROBLEMS 

1. How many foot-pounds of work does a 150-lb. man do in 
climbing a flight of stairs 10 ft. in height? How much does he do 
in descending the same flight? 

2. If a horse exerts an average pull of 100 lb. while plowing, 
how much work does he do while plowing a furrow 1 mile in length? 
If he walks at the rate of 3 miles per hour, how many foot-pounds 
of work does he do per hour? 

3. A boy carries a scuttle of coal weighing 10 Kg. up a flight 
of stairs 3 meters in height. How many kilogram-meters of work 
does he do? 

557. Time is not a Factor in Work. — Time is not con- 
sidered in determining amount of work. The amount of 
work done by a man in shoveling a ton of coal into a wagon 
is independent of the time required to do it. It requires 
neither more nor less work to plow an acre of land if the 
plowing be done in an hour or in a day. We all recognize this 
in everyday life. We are willing to pay no more for the 
shoveling of the coal or the plowing of the ground because 
the man who does the work requires a longer time in which 
to do it. In fact, we are often willing to pay a little extra 
if the work be done in the shorter time. 

558. Power, Activity or Rate of Work. — The unit in which 
power, activity, or rate of work is measured is the horse- 
power. A machine is said to be a one-horse-power machine 
when it is capable of doing 33,000 ft.-lb. of work per minute, 
or 550 ft.-lb. of work per second. This unit of power was 
chosen and named by James Watt (see Art. 599) ; he sup- 
posed that an average horse could work at about this rate. In 
order to work at this rate, however, a horse must exert an 
average pull of 125 lb. while walking at the rate of 3 miles 



476 MACHINES, WORK, AND ENERGY 

per hour, or he must exert an average pull of 150 lb. while 
walking at the rate of 2y 2 miles per hour. (Calculate.) A 
strong horse weighing 1400 lb. can stand it to work at this 
rate, 10 hours each day (see Art. 576). An average man can 
stand it to work at the rate of about ^ of a horse-power, 
eight hours each day. 

IV. MACHINES 

559. Machines and Their Uses. — Any device is called a 
machine if it is used to transfer or transform energy, or if 
it is used to change the direction, or magnitude of a force do- 
ing work (see Art. 81, Definition of Energy). 

Man uses machines for a great variety of purposes. A crow- 
bar, a set of pulleys, or a jackscrew enables a man to move a 
body whose weight is so great that he would be unable to 
move it without the use of the machine. A fishing pole en- 
ables the boy to drop his hook quietly into the pool at a point 
he otherwise could not reach; it also enables him to jerk the 
hook more quickly. The sewing machine enables a woman to 
operate the needle by moving her foot while both hands are 
free to handle the work; moreover, the needle makes several 
stitches while her foot is making a single motion (Art. 539, 
Ex. 83). The plow, the cultivator, the mowing machine, or 
the binder enables the farmer to utilize the efforts of horses. 
Steam engines, gas engines, electric dynamos and motors en- 
able man to utilize the energy in fuel at a small fraction of 
the cost of hiring the same amount of work done by men or 
even by horses (Fig. 290). Moreover, one man often operates 
such a machine while it does the work which would other- 
wise have to be done by hundreds of men. Waterwheels en- 
able men to utilize the energy in running water — energy 
which would otherwise go to waste. When this energy has 
been transformed into electricity it can be transmitted on 
wires many miles and then be used to light our homes, run 



MACHINES 



477 



our trains and street cars, and do a large portion of the 
work which has been done by men in days past (see Arts. 
587 and 592). 

560. Mechanical Advantages of a Machine. — Man uses a 
machine only when he gains some advantage by so doing. 
This advantage gained ~by using a machine is called the 
mechanical advantage of the machine. Machines may offer 
mechanical advantages of several different kinds: 















Si% 












l '-A 






J,- «... «-.,' 


Hi 




: — _is 






mjj 


■'-.'-"' ■■:.." 








w - - $ 


J 




'J& 














. - - 






"J?*lPIR*j*5ww&:MW* 


* ,"i*-' 











Fig. 



290. — A farm gasoline tractor pulling a three-bottom plow and 
doing the work of 6 or 8 horses or of 50 men. 



1. A machine has mechanical advantage of force when, 
by using it, a greater force is exerted than could otherwise 
be exerted. Examples: By using a pinchbar — a crowbar of a 
certain shape — a man is able to move a heavily loaded freight 
car which he could not move without it. By using a common 
claw hammer, a man can draw a nail which otherwise he could 
not pull. Give as many other examples as possible. 

2. A machine has mechanical advantage of speed when 
it is used to increase the speed with which the force acts. 
Examples: A fly swatter, a sewing machine, an egg beater, 
an old-fashioned spinning wheel. Name as many other ex- 
amples as you can. 



478 MACHINES, WORK, AND ENERGY 

3. A machine may have mechanical advantage op direc- 
tion or of position. Examples: By using a single fixed 
pulley the direction of the force is changed and the operator 
may choose his own position. The handle of the common 
pump, the key of the typewriter, the wheel or handle of the 
washing machine, the common door knob — all these and many 
other devices are advantageous because they aid in changing 
the direction of the applied force or they enable the operator 
to choose his position, or both. 

A machine may have mechanical advantages of two or more 
kinds at the same time. It is impossible, however, for a 
machine to have loth mechanical advantage of force and 
mechanical advantage of speed at the same time. What ad- 
vantages are afforded by the sewing machine over those of 
the hand needle ? 

561. Numerical Expression of Mechanical Advantage. — 
Mechanical advantage of force and mechanical advantage of 
speed are each frequently expressed numerically, i.e., in num- 
bers. The ratio of the force delivered by a machine to the 
force applied to the machine is said to express the mechanical 
advantage of force of the machine. 

Mechanical advantage of force = 

Number of units of force delivered 



Number of units of force applied. 

Example: A man by using a crowbar exerts a force of 

1000 lb. upon a rock while exerting a force of 100 lb. upon 

the handle of the crowbar. In this case the mechanical 

. 1000 1b. ^ 
advantage of force is — = 10. 

100 lb. 

The ratio of the speed with which the force acts to the 
speed of the applied force is said to express the mechanical 
advantage of speed of the machine. 

Mechanical advantage of speed = 

Number of units of speed of the force delivered 

Number of units of speed of force applied. 



MACHINES 479 

Example : The knives of an egg beater pass 5 times around 
a 2-in. circle while the handle on the drive wheel passes once 
around a circle of the same diameter. In this case the 
mechanical advantage of speed of the machine is 
5 X 2 X 3.1416 in. 
2 X 3.1416 in. = 5 * 
It is evident that the mechanical advantage of direction or 
position can not thus be expressed in numbers. 

562. Simple and Compound Machines. — Six simple ma- 
chines are generally recognized: The lever, the wheel and 
axle, the pulley, the inclined plane, the wedge, and the 
screw. Most machines are compound machines, i.e., they 
are combinations of two or more of the simple machines. A 
sewing machine, a typewriter, a clock, a binder, a threshing 
machine, or an automobile is made up by combining large 
numbers of simple machines. 

Exercise 85. — Study of a Compound Machine 
Examine carefully a sewing machine, a typewriter, a clock, or 
any other complex machine, noting the simple machines involved 
and how they are combined. 

563. Friction. — Friction is the resistance which opposes 
an effort to slide or roll one surface over another. Every 4 
surface is more or less rough. Even the hardest and best 
polished surfaces are found to be rough, to have uneven sur- 
faces, when examined under a magnifying glass. When we 
attempt to slide one surface over another, the rough places 
on one surface catch upon the rough places upon the other. 
This roughness of the surfaces is the cause of friction. 

The operation of any machine is affected by friction to 
some extent. (1) Oiling all moving parts which come into 
contact lessens friction. (2) In general, there is less friction 
between two surfaces of different material than between sur- 
faces of the same material. For this reason bearings are usu- 
ally made of different material from that of the axles which 
rest upon them. (3) Friction is less between two surfaces 



480 MACHINES, WORK, AND ENERGY 

when one of them rolls upon the other than when one slides 
upon the other. A ball bearing, therefore, has less friction 
than a common sliding bearing. Every boy or girl who 
rides a bicycle or uses roller skates knows that a ball-bearing 
wheel runs easier than one without ball bearings. 

Exercise 86. — A Study of Ball Bearings 

Examine the ball bearings in a bicycle or a roller skate to see 
exactly how they are constructed and how they work. 

564. The Effect of Friction on the Use of Machines. — 

We saw in Art. 550 that the length of the arms of a steel- 
yard determines the usefulness of the machine in finding the 
weight of objects. The poise at the left (Fig. 287) must be 
placed near the left end of the scale in order to balance a 
heavy object which is to be weighed. In this case there is 
very little friction and therefore the mechanical advantage 
of the steelyard may be determined by measuring this dis- 
tance from the point of support to the hook where the object 
is supported and to the point w T here the poise is placed. 

In general, though, when we use even simple machines to 
aid us in our work, we find that friction is so great that meas- 
uring the dimensions of our machine gives us but little in- 
formation as to the amount of force which must be applied to 
move an object. The term "mechanical advantage" is there- 
fore, largely of theoretical value only. If there were no such 
thing as friction, we could determine the mechanical advan- 
tage of almost any machine easily and quickly by measuring 
the size of its various parts. 

It is sometimes desirable to know approximately the force 
which must be applied to a machine in order to lift or move 
an object. We shall s.ee, however, in the following articles 
that it is far more important that we know how much work we\ 
must put into a machine in order that we may get a certain- 
amount of work out of that machine. 

565. The Law of Machines. — The work (or energy, see| 
Art. 81) put into a machine and also the work (or energy) 



MACHINES 481 

taken out of a machine must, of course, be mea'sured in 
work units, i.e., in such units as foot-pounds, or gram-centi- 
meters, or kilogram-meters. The work put into a machine 
is equal to the product of the applied force and the distance 
through which that force acts; the work delivered by a 
machine equals the product of the force delivered and the 
distance through which it acts. If there were no friction, the 
work delivered by a machine would exactly equal the work 
put into it. 

Law of Machines. — The work or energy put into a machine 
would equal the work or energy delivered by the machine — 
if there were no friction. 

566. Friction Generally Hinders but Sometimes Helps. — 
In fact, however, the work delivered by a machine is never 
exactly equal to that put into it. In most cases the work 
delivered by a machine is less than that put into it because of 
friction in the machine. Occasionally, however, a machine 
is used in such a manner as to yield an output greater than 
the input. For example, if a set of pulleys, an inclined 
plane, or an elevator is used to lower a heavy object from the 
top floor of a building to the basement, the work put into the 
machine is less than that taken out of it. Friction, in this 
case, tends to keep the body from falling; it is working with 
the operator. 

567. Efficiency of a Machine. — The efficiency of a ma- 
chine is measured by the ratio of the work (or energy) de- 
livered by a machine to the work (or energy) put into it. 

Efficiency of a machine = 

Work or energy delivered, or output 

Work or energy put in, or input 
It is generally expressed in percentage. It is usually less 
than 100 per cent, but it may be greater than 100 per cent. 
Illustrations : 

1. If a block and tackle, i.e., a set of pulleys, be used to raise 
a piano from the ground to the top floor of a building, we 



482 MACHINES, WORK, AND ENERGY 

find that we are obliged to put considerably more work into 
the machine than we get out of it. If the piano weighs 1000 
lb. and it is raised 50 ft., how much work is accomplished? 
In this case we are obliged, not only to do this amount of 
work, but we must also do work in overcoming friction. 
The efficiency of the machine in this case is not likely to 
be more than 50 to 75 per cent. 

2. Supposing now that we wish to lower the same piano 
from the top floor of the building to the ground again. If we 
use the same block and tackle we shall find that we are mot 
now obliged to put as much work into the machine as we get 
out of it. Exactly the same amount of work will be accom- 
plished in lowering the piano as was accomplished in raising 
it but the friction of the machine tends to keep- the piano> 
from falling. Friction is now aiding us — it is working with 
us. The efficiency of the machine will now probably be from 
133 to 200 per cent. 

568, Friction is Often Useful. — We generally find it an ad- 
vantage to reduce friction in a machine as much as possible ; 
sometimes, however, we find friction of great service to us. 
When we wish to haul a heavy load up a hill we make every 
effort to reduce friction. When we start down hill, however, 
we set the brakes, or possibly chain one rear wheel, in order 
to increase friction. A locomotive owes its power to pull a 
train to the friction between its drive wheels and the rails 
(Fig. 291). If this locomotive were attached to a train re- 
quiring a force of more than 60 tons to move it, the locomo- 
tive would be unable to start the train because its drive wheels 
would then slip on the rails. A bicycle or an automobile is 
likewise propelled by the friction between its wheels and the 
ground. Men working upon the ice wear ice creepers on their 
shoes to increase friction between their shoes and the ice. 
After an ice or sleet storm, horses are almost useless for haul- 
ing loads unless they are sharp shod. Why? Give as many 
cases as you can where friction is of service to us. How do 
the brakes of a railroad train bring the train to rest ? How 



MACHINES 



483 




484 MACHINES, WORK, AND ENERGY 

is friction involved in feeding the paper through a type- 
writer or printing press ? Explain how a leather belt is used 
to drive a sewing machine or a threshing machine. 

V. ENERGY AND ITS RELATION TO THE USE OF MACHINES 

569. What is Meant by Energy? — Anything which is capa- 
ble of doing work possesses energy. Energy is the capacity 
for doing work (Art. 81). Man, by putting forth effort, 
does work; therefore he possesses energy. A horse may do 
work; therefore, he possesses energy. A steam engine, as 
long as it is supplied with fuel and water and is properly 
controlled, can do work; therefore it possesses energy. The 
machine by itself, i.e., without fuel and water, can do no work. 
It is the fuel which gives it the ability to do work. The 
energy comes from the fuel, not from the mechanism of the 
engine. We have seen in Chap. VII that it is from food that 
man or the horse gets his supply of energy. 

570. Motors. — Any machine or animal used to transform 
energy into work is called a motor. A steam engine trans- 
forms the energy in coal, wood or oil into work. A gasoline 
engine transforms the energy in gasoline into work; it is a 
gasoline motor. A machine which transforms the energy 
in an electric current into work is an electric motor. To 
the extent that any man or animal simply transforms the 
energy in the food eaten into mechanical work, he is a motor. 
Agriculturists speak of the work horse as an animal motor. 

A steam engine or gasoline engine is capable of doing work 
only as long' as it is consuming fuel; as soon as it ceases to 
consume fuel it ceases to be able to do work. It is equally 
true that a man or a horse soon ceases to be able to do work 
unless supplied with food. It is the energy in the food eaten 
which enables man or animal to do work. Thus we see that 
man may differ little from a machine if he consumes food 
merely for the purpose of transforming the energy in the food 
into mechanical work. 

571. One Difference between an Animal Motor and a 



ENERGY 485 

Mechanical Motor. — While a mechanical motor, such as a 
steam engine or a gasoline engine, ceases to be able to do work 
almost at the instant that the fuel supply is exhausted, an 
animal motor can continue to do work for some time after 
its food supply is exhausted. This is because the fat and 
other tissue of the body can be converted into energy when 
necessary. Any animal, however, which is obliged to do 
hard labor without a sufficient supply of food will lose weight 
rapidly and will soon die. 

572. Efficiency of Various Motors. — Many experiments 
performed show that the average efficiency of man as a motor 
is about 20 per cent. That is, it has been found that a man 
is able to convert about 20 per cent, of the energy in the food 
be eats into mechanical work. Similar experiments show 
that the horse can also convert about 20 per cent, of the 
energy in its food into work. A steam engine will convert 
from 4 to 10 per cent, of the energy in coal into work ; there- 
fore it has from 4 to 10 per cent, efficiency. A few years 
ago in a series of tests made by the Northern Pacific Railroad 
it was found that the efficiency of its best freight locomo- 
tives was but 3.8 per cent. Good gas and gasoline engines 
have an efficiency of from 20 to 35 per cent. Electric motors 
frequently develop an efficiency of 75 to 90 per cent. From 
these figures one might conclude that the electric motor was 
the least expensive motor and that the steam engine was the 
most expensive motor for us to employ to do our work. Such 
a conclusion, however, is hasty and incorrect. The fact is that 
the steam engine is one of the least expensive motors to operate 
while the electric motor is rather expensive to operate. Can 
you suggest any reason why this should be so? Before we 
finish this chapter we shall see what the explanation really is. 

573. The Work Equivalent of a Calorie of Heat. — Many 
experiments have been made to determine the amount of 
work which is equivalent to a calorie of heat. In 1840, an 
Englishman, Joule, made such a determination. He sus- 
pended masses of iron by means of cords in such a manner 



486 MACHINES, WORK, AND ENERGY 

that they might slowly fall and in so doing revolve a set of 
paddles immersed in a vessel of water. The paddles, in stir- 
ring the water, produced friction which produced heat and 
therefore raised the temperature of the water. He noted the 
weight of the iron masses and the distance through which they 
fell. From these figures he determined the amount of work 
done. He also noted the weight of the water and the number 
of degrees of temperature through which it rose. From 
these figures, he determined the number of calories of heat 
produced. Other experimenters have used other methods of 
determining this relation. It is now known that 1 greater 
calorie (1 Cal.) (Art. 102) is equal to 3080 ft.-lb. (Art. 556) 
of work. This means that, if all the energy in food or fuel 
could be converted into work without loss, we should be able 
to produce 3080 ft.-lb. of work for every calorie of heat energy 
in the food or fuel. We have seen that it is impossible to do 
this. The horse is able to convert but about 20 per cent, 
of the energy in his food into work. Therefore we can not 
hope to secure more than about 616 ft.-lb. of work for each 
calorie (1 Cal.) of energy in the food the horse eats. 

574. Calories of Energy Needed to Do 1 Horse-power- 
hour of Work. — We have seen that 1 horse-power is the 
ability of a motor to do 33,000 ft.-lb. of work per minute 
(Art. 558). A horse-power-hour of work, then, is 60 X 33,000 
ft.-lb. or., 1,980,000 ft.-lb. Since 1 greater calorie of heat 
equals 3080 ft.-lb., we see that 640 Cal. of energy are required 
to do 1 horse-power-hour of work. A motor having an ef- 
ficiency of 100 per cent, would, then, consume 640 Cal. of 
food or fuel while doing 1 horse-power-hour of work. 

640 greater calories of heat — 1 horse-power-hour of work 

575. Cost of 1 Horse-power-day of Work by the Steam 

Engine. — One lb. of coal when burned yields from 3000 to 
3600 Cal. of heat (Art. 102). Since the average stationary 
steam engine has an efficiency of from 5 to 8 per cent., it 
utilizes only from 150 to 275 Cal. to the pound of coal. Even 



ENERGY 487 

then it requires only from 2.5 lb. to 4.5 lb. of coal to do 1 
horse-power-hour of work. In practice, a steam engine is 
considered as being in fair condition if it does 1 horse-power- 
hour of work on 4 lb. of coal. A steam engine, having the 
usual efficiency, will probably require from 25 to 35 lb. of coal 
per horse-power-day of 8 hours. The cost of this coal at 
$5.00 per ton would be from 6 cts. to 9 cts. per horse-power- 
day. (The student should verify these calculations in every 
case.) 

576. How Much Work a Horse Can Do. — King, in his 
Physics of Agriculture, says that it is commonly agreed that 
for steady and continuous work 10 hours per day, walking 
at the rate of 2% miles per hour, a horse should not be asked 
to pull (exert a force of) more than about Ho o r Vs °f its 
own weight. The work performed by horses of different 
weights would, then, be about as follows : 

Work Performed per Day by Horses of Different Weights 

Walking at the Rate of 20 Miles per Day, 

or 2 1 /2 Miles per Hour 



Weight of 






horse 


Pull exerted 


Rate of work at 2 % miles per hour 


800 lb. 


80 to 100 lb. 


0.53 to 0.67 horse-power. 


1000 lb. 


100 to 125 lb. 


0.67 to 0.83 horse-power.. 


1200 lb. 


120 to 150 lb. 


0.80 to 1.00 horse-power. 


1400 lb. 


140 to 175 lb. 


0.93 to 1.17 horse-power.. 


1600 lb. 


160 to 200 lb. 


1.07 to 1.33 horse-power. 



(The student should verify these figures.) 

577. Why the Horse Can Not Compete with the Steam 
Engine as a Motor. — We have seen that a strong horse can 
not work steadily at a rate faster than 1 horse-power. We 
shall presume that 8 hours, working at full capacity, makes a 
full length day for a horse to labor. Now, although a horse 
can convert 20 per cent, of the energy in its food into effec- 
tive work, it still is true that the food of the horse is so much 
more expensive than the fuel of the steam engine that the 
horse is quite unable to compete with the engine. 



488 MACHINES, WOKK, AND ENERGY 

The principal food of the horse is corn or oats. Smith, in 
Profitable Stock Feeding, says that a horse weighing 1200 lb. 
at severe labor, needs 16 lb. of oats and 12 lb. of hay per day. 
Other authorities give the following rule for feeding a work- 
ing horse : 1% lb. of oats or corn and 1 lb. of hay per day for 
each 100 lb. of weight. The energy in a pound of oats is 
about 1500 Cal. (see Table VII, Art. 386. Remember that 
the husk of the oat is removed in making oat meal; that the 
energy in a pound of corn is about 1650 Cal.). 

PROBLEMS 

1. We shall consider that a 1200-lb. horse is able to do 1 horse- 
power of work for eight hours per day. We shall consider his 
food as 18 lb. of oats per day, and omit any consideration of the 
hay or "roughage" consumed because the available energy in it is not 
great. What is the efficiency of this horse as a motor? 

First: 18 lb. of oats contain 18 X 1500 Cal. of energy, or 27,000 
Cal. of energy. But these 27,000 Cal. = 83,160,000 f t.-lb. of work 
(Art. 573). 

Second : 1 horse-power for eight hours = 8 X 60 X 33,000 ft.-lb. 
or 15,840,000 ft.-lb. of work. 

15,840,000 ft.-lb. 

Hence: Efficiency of the horse = = 0.19 or 19 

83,160,000 ft.-lb. 

per cent. 

What is the cost of feeding this horse? We shall suppose that 
oats are worth 50 cts. a bu. (32 lb.). The cost of 18 lb. will be 
about 28 cts. If we count the cost of the 12 lb. of hay at $15 a 
ton, we must add 9 cts. more, making the cost for feed 37 cts. per 
day. Thus we see that, considering the cost of feed and coal only, 
the horse is some four or six times as expensive as is the steam 
engine when used as a motor (Art. 575). 

How do you think that the cost of care and shelter of such a 
horse would compare with the cost of care and shelter for a 1 horse- 
power steam engine? What is true about the cost of caring for a 
horse and such an engine when they are not at work? How would 
the money invested in the horse compare with that invested in a 
1-horse-power steam engine? Do you see why all these things must 
be considered when comparing a horse with a steam engine as a 
motor? 



ENERGY 489 

578. A Man Can Not Compete with Either the Horse or 
the Steam Engine as a Motor. — It is generally agreed that a 
man of average strength can work at the rate of % to % of 
a horse-power for eight hours a day. This means that it 
requires six or eight men working one day to do a full horse- 
power-day of work. Now the cost of a man's daily food 
varies greatly, but it is probably true that the cost of food for 
a laboring man is generally somewhere from 50 cts. to $1.00 
a day. The food for a man is not nearly so great in quantity 
as that consumed by a horse nor does it contain so many cal- 
ories of heat, but it is of much finer quality, k should be much 
more varied, and it must be cooked and prepared so that its 
cost per pound is several times as great. It is probably true 
that the cost of food for the well-fed workingman is as great 
as that of the well-fed working horse. Since man can do but 
about one-seventh as much work as the horse, it is evident 
that man is an expensive motor when compared with either a 
horse or a steam engine. 

When thus considering merely the cost of the food of the 
workingman, we are entirely neglecting the cost of com- 
fortable shelter, of clothing, of reading matter, of traveling 
expenses, of amusements, and all the other elements of higher 
living which make life really worth while. Moreover, the 
laboring man is usually the head of a family and therefore 
must provide food, shelter, clothing, school books, and all 
the other necessities of life for the several members of his 
family. When we consider all these things, we see clearly 
that no working man can possibly compete with other forms 
of motors. He must labor at tasks which other motors are 
unable to perform. 

Cost of 1 Horse-power-day of Work, Considering Fuel and 

Food Only 

By steam engine 6 to 9 cts. 

By gasoline engine 15 to 20 cts. 

By horse 40 to 50 cts. 

By man $4.00 to $8.00 



490 MACHINES, WORK, AND ENERGY 

579. Why We often Use the Horse instead of the Steam 
Engine. — The horse not only does useful work, but while do- 
ing it he is obliged to do a large amount of useless work. The 
stationary engine does no useless work in moving its own mass 
through space. One of the reasons why the efficiency of the 
stationary engine is greater than that of the locomotive is that 
the locomotive does a large amount of useless work in trans- 
porting its own mass. 

There are many kinds of work, however, which can be done 
at a lower cost by the horse than by the steam motor. In 
excavating for a house or in grading up around the house 
after it is built, for most hauling about the farm, for the 
delivery of grain to the local market, for the cultivating and 
the harvesting of crops on the ordinary farm, the horse is 
still often the most practical motor we have. 

580. Why We often Employ the Labor of Man instead of 
the Horse or the Steam Motor. — Just as we still employ the 
horse instead of the steam engine to do many kinds of work, 
so in spite of the high cost of his labor we still find it profitable 
to employ man to do much of our work. In the construction 
of buildings there will probably always be a demand for 
laborers to handle the brick and mortar, and the wheel- 
barrow and spade, as well as to handle the hammers, the saws, 
the planes, and the trowels. In most lines of work there is 
some rough work which might possibly be done by machines 
but which can at present be more cheaply done by the cheap- 
est of human labor. More and more, however, work of this 
nature is being done by other motors and man is finding that 
he must prepare himself for doing such work as requires 
thoughtful, intelligent action. 

VI. SOME COMMON MECHANICAL MOTORS 

581. Common Mechanical Motors. — In the last section we 
saw that, while man and the horse were both more efficient 
motors than the steam engine, it still is true that the steam 
engine is a much less expensive motor to operate — that the 



SOME COMMON MECHANICAL MOTORS 491 

most efficient motor is not necessarily the least expensive ta 
employ. In this section we shall study briefly the principles 
of some of the more common mechanical motors. 

Nearly all power used today to run the machinery in 
factories and mills and about mines, to pump the water for 
city water systems, and to light city streets and homes by 
electricity, to propel ships at sea, and railroad and interurban 
trains on land, to run street cars and automobiles — m fact, 
to operate machinery for any purpose — is derived from a 
few different kinds of mechanical motors. These motors are 
(1) water motors, (2) steam motors, (3) gas motors, includ- 
ing gasoline or crude oil motors, and (4) electric motors. 





Fig. 292. — The overshot water wheel. Fig. 293. — The breast wheel. 

Water Motors 

582. Kinds of Waterwheels. — Running and falling water 
has been used since the beginning of civilization to produce 
power and do work for man. Waterwheels of different kinds 
have been used. Overshot, breast, and undershot wheels 
are the older types, while the impulse and turbine wheels 
are of recent origin. 

583. Overshot Wheels. — Overshot wheels have generally 
been used when a small stream having a considerable fall is 
available (Fig. 292). Why? Such wheels are sometimes 50 
or 60 ft. in diameter and may develop an efficiency of 80 or 
90 per cent. How is the power produced by such a wheel? 

584. Breast Wheels. — Breast wheels are generally used 
when a larger flow of water is available but less fall can be 



492 MACHINES, WORK, AND ENERGY 

secured (Fig. 293). How does this wheel differ from the 
overshot wheel? The efficiency of the breast wheel is usu- 
ally less than that of the overshot wheel. Can you see why 
this should be so ? 

585. Undershot Wheels. — Undershot wheels are used 
when only a slight fall of water is obtainable (Fig. 294). 
While the weight of the falling water is the principal source 
of power in the overshot and breast wheels, in the case of the 
undershot wheel, the force of the impact of the water against 
the blades or paddles is the chief source of power. Under- 
shot wheels frequently have low efficiency. Why is this so? 





Fig. 294.— The undershot Fig. 295.— The Pelton wheel or 

wheel. impulse wheel. 

586. Impulse Wheels. — Impulse wheels are used when 
there is a small supply of water but available under a great 
"head" or pressure. Frequently small streams or lakes lo- 
cated high up in a mountain may be utilized for power pur- 
poses. In such cases the water is often conveyed down the 
mountain side in strong iron pipes. At the foot of the moun- 
tain, the water under high pressure is permitted to escape 
through a nozzle at high velocity. This stream is directed 
against cup-shaped buckets on the rim of the wheel (Fig. 
295). After striking the buckets, the water falls to the 
ground robbed of its energy. 

These wheels have some advantages over other kinds of 
waterwheels: They can easily be changed in location. They 
are small compared with other wheels for the amount of 



SOME COMMON MECHANICAL MOTORS 



493 



power they are able to produce. One such, wheel constructed 
several years ago was but 3 ft. in diameter and received its 




Fig. 296. — General view of the Mississippi River, the .locks, the power 
house and the dam at Keokuk. The power plant is capable of pro- 
ducing 300,000 horse-power. It cost $25,000,000. 




Fig. 297. — Interior view of the power house at Keokuk showing the 
15 generators now installed, each of which produces 10,000 horse-power 
of electrical energy. 



supply of water from a stream 2100 ft. above the wheel. The 
diameter of the nozzle was but % in. and yet the wheel did 



494 



MACHINES, WORK, AND ENERGY 



100 horse-power of work. The efficiency of impulse wheels 
is frequently 80 or 90 per cent. 




Fig. 298. — Vertical cross section of the turbine pit. 




Fig. 299. — Horizontal cross section of the turbine pit. 

587. Turbine Wheels. — Turbine wheels are now generally 
taking the place of the older types of wheels. The water 



SOME COMMON MECHANICAL MOTORS 



493 



power at Niagara Falls as well as that of the Mississippi 
.Eiver at Keokuk, Iowa (Fig. 296), is developed by means of 
turbine wheels. At Niagara they operate under a "head' r 
of about 170 ft. and at Keokuk with a "head" of about 30 
ft. At the present time 500,000 horse-power is developed at 
Niagara Falls and 150,000 horse-power at Keokuk (Fig. 297). 
The turbine wheel is placed at the bottom of a cylindrical 
well or pit. The water at the bottom of the well is under 
high pressure and is forced horizontally through spaces be- 





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Fig. 300. — One of the turbine wheels in the Keokuk power plant. It 
hangs on the bottom of a steel shaft over two feet in diameter and turns 
one of the 10,000 h.p. generators shown in Fig. 297. 

tween fixed or stationary vanes set at a certain angle (Figs. 
298 and 299). The water strikes against the vanes or blades 
of the movable wheel causing it to rotate (Fig. 300). After 
its energy is expended upon the vanes of the movable wheel, 
the water drops into the outlet, or tailrace. A shaft which 
revolves with the wheel extends upward above the surface 
of the water where it runs a dynamo or other machinery. 



496 MACHINES, WORK, AND ENERGY 

Turbine wheels are generally used where a large flow of water 
under a moderate "head" is available. They often give an 
efficiency of 80 or 90 per cent. 

Source of All Energy 

588. The Sun is the Source of All Energy. — The original 
source of the energy in water power is the sun. "We have 
seen that water is constantly evaporating when exposed 
to the air. Evaporation is constantly taking place from 
every body of water, from every moist surface, and from 
the leaves of plant life (Art., 12 and 176). We 
have also seen that evaporation always means the absorption 
of heat and the production of cold (Art. 178). It would 
seem, therefore, that this constant evaporation ought to result 
in the lowering of the temperature of the earth's surface. 
Moreover, the heat of the earth 's crust is constantly radiating 
through the atmosphere into space. "Why, then, does not 
the earth's surface become so chilled that all of the water 
upon it is frozen and all life disappears? See Chap. IY, 
Arts. 219 to 223, for your answer. Eeview the cause 
of precipitation, i.e., of rain and snow. The source of 
energy in running and falling water is the elevation of water 
by evaporation and the distribution of the water vapor over 
the earth 's surface by winds, both of which are due to energy 
from the sun. 

We have seen that the energy in all plant and animal life 
is also originally obtained from the sun (Chap. VII, Art. 373). 
Coal is known to be the product of the remains of plant life 
long ago buried in the earth's crust. Geologists tell us that 
petroleum also is the result of decomposed plant and animal 
matter which was buried ages ago. The sun is the original 
source of all stored-np energy which man may use to produce 
power. 

589. Water Power, the Cheapest of All Power. — Water 
power is today the least expensive of all available power. So 
long as the sun continues to pour its energy down upon the 



SOME COMMON MECHANICAL MOTORS 



497 



earth, so long will evaporation continue to take place, the 
rain will continue to fall, and running water will be available 
to do work for mankind. The largest expense connected with 
obtaining power from running water is the cost of construct- 
ing the necessary dams and installing the machinery of the 
plant. This often requires a large outlay of capital. The 
cost of producing the power after the plant is once installed 




Fig. 301. — Distribution of water power of United States. The heav- 
ily shaded portions show the regions where water power is easily avail- 
able; the horizontally shaded portions, where hydro-electric power is; 
easily available; the vertical shading, where hydro-electric power is pos- 
sibly available. 

is small. When man wishes to obtain power from coal or 
petroleum, he must first raise them to the earth's surface, 
and this requires much labor and expense. 



Available Water Power of the United States 

590. Amount of Water Power Available. — The govern- 
ment has estimated that there is sufficient available water 



498 MACHINES, WORK, AND ENERGY 



>ry 



power in the United States, if it were utilized, to run every 
machine in all our factories and mills, to propel all our rail 
road trains, street cars, and automobiles, to light all our 
streets and homes — in fact to operate every machine in the 
United States. Only about one-fifth of this power is, how- 
ever, now being utilized, the rest is running to waste. About 
50,000,000 h»orse-power is now required in the United States 
for power purposes. About 10,000,000 horse-power of water 
power has thus far been developed. The use of water power 
is, however, growing rapidly. 

591. Distribution of Water Power. — One of the principal 
reasons why so small a portion of our available water power 
has been developed is the fact that generally water power can 
be developed only in mountainous, or at least, in hilly regions. 
Why ? Most of the water power thus far developed is located 
in New England, New York, and Pennsylvania; along the 
Appalachian Mountains from Georgia northward; in Michi- 
gan, Wisconsin, and Minnesota; and along the Kocky and 
Sierra Nevada Mountains in the west (Pig. 301). The larg- 
est power plants in the United States are those at Niagara 
Falls and on the Mississippi Eiver at Keokuk, Iowa. Much of 
ihe available water power is located some distance from the 
;great manufacturing centers where it would be most useful. 

592. Transmission of Power. — Recently it has been found 
possible to transmit energy in the form of electric current a 
distance of 200 miles with profit. On the map (Fig. 301), 
a circle with a 200 mile radius has been drawn about the 
power plants at Niagara Falls and at Keokuk, Iowa. Any 
point lying within these circles may easily be supplied with 
power from these plants. St. Louis, Missouri, 137 miles dis- 
tant, is now consuming the larger portion of the power gen- 
erated at Keokuk (Fig. 302). Much of the power gener- 
ated at Niagara Falls is sold in the cities of western New 
York. Many of the cities on the coast of California receive 
practically all their power from hydro-electric plants lo- 
cated many miles distant in the Sierra Nevada Mountains. 



SOME COMMON MECHANICAL MOTORS 



499 



The Steam Engine 
593. Importance of the Steam Engine. — No other device 
or machine invented by man has had as great an influence 
upon the material advancement of civilization as has the 




Fig. 302. — Line for transmission of electric power from Keokuk to 

St. Louis. 



steam engine. It is estimated that the steam engines of the 
world are today doing from 150 to 200 million horse-power of 
work. This is many times the amount of work the entire 
population of the civilized world could do were every adult 
human being working daily at hard manual labor. The steam 



500 



MACHINES, WORK* AND ENERGY 



engine during the last century has largely freed civilized man 
from hard labor. It has made possible the mine, the mill, the 
factory, the steam ship, and the railroad. It has made man 
almost the complete master of the physical forces of the 
world. 

594. Use of the Earliest Steam Engines. — It was just at 
the beginning of the 18th century (1700) that the steam 
engine first began to be recognized as a useful machine. 
During the 18th century, however, practically the only use 
to which it was put was the pumping of water from the mines 
of England. Before the invention of the steam engine many 




Fig. 303. — Fulton's steamboat, Clermont. 
(From Stories of Useful Inventions. Cour- 
tesy of the Century Company.) 



Fig. 304.— The Rocket. 
( From Hoadley's Essen- 
tials of Physics. Courtesy 
of American Book Co.) 



of the coal mines were frequently flooded and some were actu- 
ally abandoned. 

It was not until the closing years of that century that 
people really began to believe that the steam engine could be 
used successfully for other purposes. It was about 1785 that 
the first experimental steamboats were made and not until 
1807 that Fulton made the Clermont (Fig. 303), the first 
really successful steamboat. It was not until 1825 that Ste- 
venson constructed the Eocket (Fig. 304), the first successful 
locomotive. Today the steam engine is probably doing three- 
fourths of the work done in the civilized world. 



SOME COMMON MECHANICAL MOTORS 



501 



595. Source of Power in the Steam Engine.— When water 
is changed into steam it expands about 1600 times in volume ; 
a cubic inch of water becomes nearly a cubic foot of steam. 
If the boiling water and steam are confined in a closed vessel, 
a boiler, the steam soon develops great pressure and it is this 
pressure which is utilized in the steam engine. 




Fig. 305. — The Newcomen air-steam engine, 1705. 

596. The Newcomen Air-steam Engine. — Although several 
devices using steam had earlier been invented, the first really 
useful engine was invented by an Englishman named New- 
comen in 1705. The Newcomen engine, however, was an 
air-steam engine; in fact, it was not steam pressure but air 
pressure which actually did the work. For about three- 
quarters of a century, or until about 1874, this air-steam 
engine was the only type known and used. 

597. Principle of the Newcomen Engine. — The principle 



502 MACHINES, WORK, AND ENERGY 

of this engine is shown in Fig. 305. The only use to which 
this engine was put was pumping water. The pump-rod and 
piston were balanced at the two ends of a beam, /, which was 
free to rotate on its axis, V. The piston moved up and down 
in the cylinder. When the valve, D, was opened, steam 
rushed into the cylinder as the piston moved up and the 
pump-rod descended. The valve, D, was now closed and the 
valve, F, opened. This permitted a spray of cold water 
from the tank, G, to enter the cylinder. This spray of cold 
water condensed the steam in the cylinder, producing a 
vacuum in the cylinder beneath the piston. The air pressure 
upon the upper surface of the piston then forced the piston 
down to the bottom of the cylinder. This raised the pump- 
rod and plunger. This was the working stroke. The water 
spray was then cut off and the water and condensed steam 
drained off into the reservoir, R, which had to be placed 
about 30 ft. below the cylinder. Do you see why? [Review 
air pressure (Arts. 150-152) and pumps (Art. 483 to 486).] 
The valve, D, was again opened, the spray of water again ad- 
mitted and a second stroke was completed. 

598. Humphrey Potter's Invention. — At first the valves, 
D, and F, were operated by hand. It was an easy task and a 
boy did the work. Only about six or eight strokes were usu- 
ally made each minute. It is recorded that an ingenious 
boy, Humphrey Potter, in 1713, tiring of this task, contrived 
a system of levers and strings fastened to the moving beam 
in such a manner as to operate the valves automatically (Fig. 
306). This boy's invention doubled the amount of work 
which the engine could do, for the valves were now opened 
and shut exactly at the right moment. With this improve- 
ment the Newcomen engine made 15 or 16 strokes each minute. 
But at its best this engine was extremely wasteful of fuel. It 
required 35 to 50 lbs. of coal to do a horse-power-hour of 
work, some eight to ten times as much as is required by steam 
engines today (see Art. 575). 

599. Watt's Improvement. — It remained for James Watt, 



SOME COMMON MECHANICAL MOTORS 503 

a Scotchman, to perfect the steam engine. About 1774, Watt 
so perfected the steam engine that it became practically the 
engine of today. He discovered the chief source of energy 
loss in Newcomen's engine and overcame it. He saw that 
the chief difficulty with Newcomen's engine was the loss of 
heat energy about the cylinder. He was determined to re- 
duce this loss; to do so he made three important improve- 
ments : 



Fig. 306. — Humphrey's latches and strings. (From Stories of Useful 
Inventions. Courtesy of the Century Company.) 

First, Watt saw that the spray of cold water forced into 
the cylinder at each stroke so cooled the cylinder and piston 
that a large amount of the energy in the steam admitted at the 
next stroke was consumed in reheating the cylinder. He 
therefore provided for the condensation of the exhaust steam 
in another vessel (E, Fig. 307) which was constantly sur- 
rounded by cold water. He also surrounded the cylinder 
with a jacket of steam. 

Second, Watt made his an all-steam-engine whereas New- 



504 



MACHINES, WORK, AND ENEEGY 



comen's was an air-steam engine. His purpose in doing so 
was to keep the cylinder hot. The upper end of the cylinder 
of Newcomen's engine was open to the air and air pressure 
was used to force the piston down. The piston and cylinder 
were, therefore, constantly losing heat to the air. "Watt 
closed both ends of the cylinder of his engine and made the 
piston rod work through a stuffing box, a small opening 







Fig. 307. — Watt's engine. 

packed steam-tight, just as steam engines are constructed to- 
day. 

Third, Watt's third improvement was to use oil to lubricate 
the piston and prevent the steam from passing it. It was 
impossible in those days for mechanics to make the pistons 
and cylinders as true and close fitting as they are made 
today. To prevent the steam from escaping past the piston 
as well as to lubricate it, Newcomen kept a stream of water 
running constantly upon the upper surface of the piston of 
his engine (Fig. 305). This water absorbed a large amount 
of the heat from the steam. 



SOME COMMON MECHANICAL MOTORS 505 

These improvements by Watt greatly increased the ef- 
ficiency of the steam engine. It now did the same amount of 
work while using but about one-fourth as much coal as New- 
comen 's engine used. "We must remember that Watt 's motto 
was: ''Keep the cylinder and piston as hot as possible all the 
time/' a rule which is followed in all steam-engine construc- 
tion today. 

600. How Watt's Engine Worked. — In Watt's engine the 
steam entered through the pipe (D, Fig. 307). Just as the 
piston reached the top of the cylinder the valves C and F, 
were opened and the valve, E, closed. The opening of the 
valve, 0, permitted the steam to flow into the cylinder above 
the piston forcing it downward. The opening of the valve, 
F, permitted the steam in the cylinder below the piston to 
escape into the vessel, H, where it was condensed by the 
surrounding cold water. The condensation of this steam 
tended to produce a vacuum in the lower portion of the cylin- 
der. The steam also entered the jacket surrounding the 
cylinder ; thus the cylinder was always kept hot. Just as the 
piston reached the bottom of the cylinder the valves, C and F, 
closed and the valve, E, opened. The steam could then no 
longer enter from the pipe, D, but it could flow through the 
pipe, X, from the upper portion of the cylinder into the lower 
portion. The pressure was now the same on both sides of the 
piston and the weight of the pump-rod pulled that end of the 
beam down and so raised the piston again to the top of the 
cylinder. The valves were operated by the pins, M, M, M, on 
the rod N. The water formed by the condensation of steam 
was forced by the pump, 7, into the hot well, K. The pump 
ui', raised this warm water from the hot well and forced it 
into the boiler again through the pipe, B. 

601. Watt's Double Acting Engine. — While the engine 
just described was by far the most economical and effective 
engine which had ever been made, still, Watt was not satis- 
fied. Live steam, i.e., steam under full pressure, entered only 



506 



MACHINES, WJORK, AND ENERGY 



one end of the cylinder and actually did work only while 
forcing the piston downward. About 10 years later, 1784,, 
Watt invented a double acting engine, i.e., one in which the 
steam under full pressure entered first one end of the cylinder 
and then the other. In this way the piston was forced first 
to one end of the cylinder and then the other end by the live 
steam. 

602. The Modern Steam Engine. — The Construction and 
operation of the modern steam engine is shown in Fig. 308. 




Fig. 3*08. — The modern steam engine. 



The governor controls the speed of the engine by controlling 
the rate at which the steam enters the cylinder. The gov- 
ernor belt running from -the shaft of the flywheel causes the 
governor to revolve. As the speed increases, the heavy balls, 
owing to centrifugal force (Art. 542, Ex. 84), tend to swing 
farther out, i.e., revolve in a larger circle. As they do so they 
force the cut-off valves down, thus reducing the flow of steam. 
As the flow of steam decreases, the force with which the piston 
is driven becomes less and the speed of the flywheel is less- 
ened. As the speed of the flywheel becomes less, the cut-off 



SOME COMMON MECHANICAL MOTORS 



507 



valves again rise admitting more steam. Thus the speed of 
the engine is automatically controlled. 

After passing the governor cut-off valves, the steam enters 
the steam chest, 8-C. From the steam chest it passes through 
the port, P, into the right-hand end of the cylinder. The 
steam pressure then forces the piston to the left. The steam 
in the left end of the cylinder escapes through the other port, 
P, to the exhaust, E, whence it escapes to the air or the con- 
denser. 





Fig. 309. — An upright boiler 
with casing cut away, showing 
the tubes. 



Fig. 310. — An upright boiler 
with the engine attached to the 
side of the boiler. 



An ingenious device called the eccentric on the shaft of 
the flywheel operates the slide valve, S-V. Just as the piston 
reaches the left end of the cylinder, the slide valve is moved 
far enough to the right to admit the steam to the left end of 
the cylinder and allow the steam in the right end of the 
cylinder to escape through the exhaust. 



508 MACHINES, WORK, AND ENERGY 

The Gas Engine 

603. The Internal Combustion Engine. — We have seen 
that in the case of the steam engine the fuel is burned beneath 
the boiler, producing steam which is then conveyed to the 
engine. It is evident that the boiler may be located some 
distance from the engine. In gas engines, however, the fuel 
is burned within the cylinder of the engine. Such engines 
are, therefore, called internal combustion engines. 

604. The Fuel of Internal Combustion Engines. — Such 
engines may burn almost any kind of combustible gases. 
Everybody is somewhat familiar with such engines burning 
gasoline and used in automobiles or on farms. But internal 
combustion engines, or gas engines as they are commonly 
called, may also use as fuel natural gas, coal gas, water gas, 
kerosene, crude petroleum, or alcohol. 

605. The Earliest Gas Engines. — The first really success- 
ful internal combustion engines burned gasoline. They were 
made in France and Germany in 1861 and 1862. The first 
successful gas engines made in the United States were made 
in 1873. 

606. Importance of the Gas Engine. — For many years 
these engines were not of great importance. They were then 
used only where small amounts of power were needed occa- 
sionally and in places where other power was not easily 
obtainable. In recent years, however, engines burning gaso- 
line, crude petroleum, and gas produced from coal, as a waste 
product from blast furnaces, have become of great importance. 

607. The Gasoline Engine and the Automobile. — Many 
attempts have been made during the past two centuries to 
produce self-propelled vehicles adapted to use on public 
streets and country roads (Fig. 311). Until the gasoline 
engine was perfected little progress was made in this direc- 
tion. The ordinary steam engine was found to be too heavy 
and cumbersome to be easily adapted to this use. The mod- 
ern gasoline engine for use in automobiles weighs but about 



SOME COMMON MECHANICAL MOTORS 



500 



10 or 15 lbs. to the horse-power ; moreover, it is ready for use 
at all times and can be started at a moment's notice. The 




Fig. 311. — Cugnot's steam carriage, 1769. (From Stories of Useful In- 
ventions. By Courtesy of the Century Company. ) 




Fig. 312. — The Langley aeroplane flying, May 28, 1914. 

chief advantages, then, of the gasoline engine for this purpose 
are its comparative lightness and the fact that no time need 
be lost in heating it ready for service. 



510 



MACHINES, WORK, AND ENERGY 



608. Gasoline Motors and Aeroplanes. — For many cen- 
turies men have looked forward to the day when they should 
be able to navigate the air, to fly as birds do. Experi- 
menters realized the necessity of producing a motor of great 
power with as little weight as possible. Before the end of the 
last century, in 1896, Prof. Langley at Washington, D. C, 
constructed a steam-driven flying machine which flew with- 
out a passenger several times, once more than a half mile over 





Fig. 3 13.— First 
cycle, diagram. Suc- 
tion stroke. 



Fig. 3 1 4.— First 
cycle, engine. Suc- 
tion stroke. 



the Potomac River before its fuel supply was exhausted and 
it fell of its own weight into the water. 1 All attempts to 
produce a successful " heavier-than-air " flying machine failed 
until the gasoline engine was highly perfected. Every other 
type of motor has proved too heavy for the power it could 

1 It is an interesting fact that two attempts were made in 1904 to 
prove that Langley's aeroplane could fly while carrying a pilot. Upon 
both occasions, however, the machine plunged into the river as quickly 
as it was launched. It is now known that the trouble lay partly in 
the inexperience of the pilot. On May 28, 1914, Glenn Curtis, an 
experienced flyer, made a successful flight with the Langley aeroplane 
which had rested for years in the archives of the Smithsonian Institute 
and had been styled "Langley's Folly" (Fig. 312). 



SOME COMMON MECHANICAL MOTORS 



511 




Fig. 315. — Second 
cycle, diagram. Com- 
pression stroke. 




Fig. 316.— Second 
cycle, engine. Com- 
pression stroke. 















1 


• 




















• 


1 






Fig. 3 1 7.— Third 
cycle, diagram. Work- 
ing stroke. 




Fig. 3 18. 
cycle, engine, 
ing stroke. 



- Third 
Work- 



512 



MACHINES, WORK, AND ENERGY 



produce. Gasoline motors now used on aeroplanes are mar- 
vels of lightness and power. Such engines usually weigh but 
from 3 to 5 lbs. per horse-power. 

609. How the Gas Engine Works. — Like Newcomen's air- 
steam engine, the gas engine cylinder is closed only at one 
end. The mixture of gas and air is admitted into the closed 
end of the cylinder and then ignited. Kapid combustion 
takes place, producing very high temperature thus expanding 
the gases greatly. The pressure produced drives the piston 
to the opposite end of the cylinder. 





Fig. 319.— Fourth 
cycle, diagram. Ex- 
haust stroke. 



Fig. 320.— Fourth 
cycle, engine. Ex- 
haust stroke. 



610. The Four-cycle Engine. — Most gas engines are of the 
type known as four-stroke or four-cycle engines. By this 
is meant that the piston moves the length of the cylinder four 
times and the flywheel makes two revolutions for each explo- 
sion of gas. The operation of the engine is as follows : 

First Stroke: The piston moves from the closed end of the 
cylinder to the open end. This produces a partial vacuum, 
and suction causes air charged with a gaseous fuel or a mix- 
ture of air and gas to rush in through the intake valve (Figs. 
313 and 314). 



SOME COMMON MECHANICAL MOTORS 513 

Second Stroke: The piston moves from the open end of 
the cylinder to the closed end. This compresses the charge of 
fuel and air to from one-fourth to one-fifteenth of its original 
volume, depending upon the kind of fuel used (Figs. 315 and 
316). 

Ignition: Just at the end of the second stroke the charge is 
ignited, usually by an electric spark. 

Third Stroke: This is the expansion or working stroke. 
The burning gases produce great pressure upon the piston and 
drive it toward the open end of the cylinder (Figs. 317 and 
318). 

Fourth Stroke: The exhaust valve is opened and as the 
piston returns to the closed end of the cylinder it forces the 
products of combustion out through the exhaust port (Figs. 
319 and 320). 

The four strokes are (1) suction stroke, (2) compression 
stroke, (3) working stroke, (4) exhaust stroke. These four 
strokes constitute one complete cycle or round of action. 

6n. Purpose of Compression. — The purpose of com- 
pressing the gas before igniting it is to secure the most rapid 
combustion possible. The gas in the cylinder is much like 
brush in a brush heap. If we wish the brush to burn rapidly 
we must tramp it down into a compact mass. The more com- 
pact the brush, the more rapidly it burns and the hotter the 
fire. In like manner the compression of the gas in the cylin- 
der produces more rapid combustion, and hence a higher tem- 
perature. Greater pressure on the piston results. 

6 1 2. Compression Must Not be too Great. — Whenever a 
gas is compressed heat is produced. The pump becomes hot 
when we "pump up" a bicycle or automobile tire. In com- 
pressing the gas in the cylinder of a gas engine, care must be 
taken that the temperature of the gas is not raised to the 
kindling temperature (see Art. 77) before the end of the 
compression stroke. "What would be the result if the gas 
were ignited during the second stroke? How would this 
affect the power of the engine? 

613. Compression for Different Gases. — Different fuels 
require different amounts of compression to produce the 



514 



MACHINES, WORK, AND ENERGY 



largest amount of power. In practice, the different gases are 
compressed about as follows: 

Kerosene, compressed to about M to % of its original volume, 
Gasoline, compressed to about V& to % of its original volume, 
Alcohol, compressed to about ~Vio to %5 of its original volume, 
Natural gas, compressed to about Vi to Vw of its original volume, 
Coal gas, compressed to about Vg to Ho of its original volume. 

614. Keeping the Cylinder Cool. — We saw that "Watt, 
when developing the steam engine, adopted the motto, ' ' Keep 
the cylinder as hot as possible. " With gas engines, however, 
the danger is that the cylinder will get too hot — hot enough 
to ignite the gas too soon. The cylinders of small gas engines 
are sometimes cooled by air, a fan forcing the air past the 
cylinder. Such engines are called air-cooled engines. All 
large gas engines are water-cooled engines. The cylinders 
of water-cooled engines are surrounded by jackets similar to 
the jackets Watt used on his steam engines. But in this case 
the jacket contains flowing water to keep the cylinder cool 
instead of steam to keep the cylinder hot. 

615. Need of the Heavy Flywheel. — We have seen that 
in the four-cycle engine, force is be- 
ing exerted upon the piston but one- 
fourth of the time, i.e., during the 
third stroke. But the engine must 
continue to work all the time. We 
should therefore expect the engine 
to run with an unsteady motion. 
It would do so were it not for the 
the heavy flywheels. The heavy fly- 
wheels absorb a large amount of en- 
ergy during the working stroke and 
give it up again during the other FlG< 32 i._How several 
three strokes. Being massive they cylinders produce a con- 

. „ , . -. stant, steady power. 

have great capacity for holding 

energy and therefore vary but little in speed during the cycle. 







/>^J/N/-\|/^ 



O/VE CYLINDER 



FOUR C Y LINGERS 



SIX CYLINDERS 



a^ . 4r^ . ^4r - a ^ 



H 



EIGHT CYLINDERS 



H 



TlVEL YE CYLINDERS 



MACHINES, WORK, AND ENERGY 515 

6 1 6. Many-cylindered Engines on Automobiles. — It is 

undesirable to load an automobile with heavy flywheels, al- 
though a steady motion is very desirable. For this reason 
nearly all gasoline engines used on cars are constructed with 
several cylinders. The pistons of the four-cylinder engine 
are connected with the drive shaft in such a manner that, 
while one piston is performing the first stroke, another is per- 
forming the second stroke, the third piston the third stroke, 
and the fourth the fourth stroke. Thus we see that some one 
of the pistons is at work every instant. This produces a 
steady motion. In the six-cylinder, eight-cylinder, and 
twelve-cylinder engines the power is still more nearly con- 
stant (Fig. 321). 



APPENDIX 

WEIGHTS AND MEASURES 
ENGLISH SYSTEM 

LINEAR MEASURE OR MEASURES OF LENGTH 

12 inches (in.) =1 foot (ft.) 

3 feet = 1 yard (yd.) 

5H yards = 1 rod (rd.) 

163^ feet = 1 rod 

320 rods = 1 mile (mi.) 

1760 yards = 1 mile 

5280 feet = 1 mile 

SQUARE MEASURE OR SURFACE MEASURE 

144 square inches (sq. in.) = 1 square foot (sq. ft.) 

9 square feet = 1 square yard (sq. yd.) 

30 14 square yards = 1 square rod (sq. rd.) 

160 square rods = 1 acre (A.) 

1 square mile = 1 section 

36 square miles, or 36 sections = 1 township 

CUBIC MEASURE OR MEASURE OF VOLUME 

1728 cubic inches (cu. in.) = 1 cubic foot (cu. ft.) 
27 cubic feet (cu. ft.) =1 cubic yard (cu. yd.) 

AVOIRDUPOIS WEIGHT 

27.34 grains (gr.) = 1 dram (dr.) 

16 drams = 1 ounce (oz.) 

16 ounces = 1 pound (lb.) 

100 pounds = 1 hundredweight (cwt.) 

2000 pounds = 1 ton (T.) 

2240 pounds = 1 long ton 1 

4373^2 grains = 1 ounce 

7000 grains = 1 pound 

1 The long ton is used at the United States custom houses and often in wholesale 
transactions in coal and iron, as well as being in general use in Great Britain. 

517 



518 APPENDIX 

MEASURES OF TIME 

60 seconds (sec.) = 1 minute (min.) 

60 minutes = 1 hour (hr.) 

24 hours = 1 day (da.) 

7 days = 1 week (wk.) 

365 yi days, or 12 months = 1 year (yr.) 

10 years = 1 decade 

10 decades, or 100 years = 1 century 

UNITED STATES LIQUID MEASURE 

4 gills (gi.) = 1 pint (pt.) 231 cubic inches = 1 gallon 

2 pints = 1 quart (qt.) 31^2 gallons = 1 barrel (bbl.) 

4 quarts = 1 gallon (gal.) 57.75 cubic inches = 1 liquid quart 

UNITED STATES DRY MEASURE 

2 pints (pt.) = 1 quart (qt.) 32 quarts = 1 bushel 

8 quarts = 1 peck (pk.) 67.2 cubic inches = 1 quart 

4 pecks = 1 bushel (bu.) 2150.4 cubic inches = 1 bushel 

HOUSEHOLD MEASURES (APPROXIMATE VALUES) 

1 drop = Yio cubic centimeter 

1 teaspoonful = 5 cubic centimeters 
. 1 tablespoonful = 3 teaspoonfuls 

16 tablespoonfuls = 1 cup 

2 cups = 1 pint, liquid 

1 pint, liquid = 473.1 cubic centimeters 
1 pint, dry — 550.5 cubic centimeters 

MISCELLANEOUS 

1 United States gallon of water weighs 8.33 pounds 

1 cubic foot of water weighs 62.3 pounds 

1 cubic foot of dry air at sea level weighs 1 .23 ounces 

1 gallon of gasoline weighs about 6 pounds 

The average air pressure at sea level = 1033 grams per square centimeter, 

or 14.7 pounds per square inch 
1 horse power = 550 foot-pounds per second or 33,000 foot-pounds per 

minute 
1 greater calorie (l cal.) = 3080 foot-pounds 
1 horse power-hour = 1,980,000 foot-pounds 
1 horse power-hour = 640 greater calories 
1 pound of coal yields from 3000 to 3200 greater calories of heat 



APPENDIX 519 

METRIC SYSTEM 

LINEAR MEASURE OR MEASURES OF LENGTH 
10 millimeters (mm.) = 1 centimeter (cm.) 
100 centimeters = 1 meter (m.) 

1000 meters = 1 kilometer (km.) 

SQUARE MEASURE OR MEASURES OF SURFACE 

100 square millimeters (sq. mm.) = 1 square centimeter (sq. cm.) 
10,000 square centimeters = 1 square meter (sq. m.) 

1,000,000 square meters = 1 square kilometer (sq. km.) 

MEASURES OF VOLUME OR CAPACITY 

1,000 cubic millimeters (cu. mm.) = 1 cubic centimeter (cu. cm.) 
1,000,000 cubic centimeters = 1 cubic meter (cu. m.) 

1,000 cubic centimeters = 1 liter (1.) 

MEASURES OF WEIGHT OR MASS 

1000 milligrams (mg.) = 1 gram (g. or gm.) 

100 centigrams (eg.) = 1 gram 
1000 grams = 1 kilogram (kg.) 

1000 kilograms = 1 metric ton 

MISCELLANEOUS 

1 cubic centimeter of water at 4°C. or 39.2°F. weighs 1 gram 

1 liter of water at 4°C. or 39.2°F. weighs 1 kilogram 

1 cubic centimeter of dry air at the sea level weighs 0.001293 grams 

1 liter of dry air at the sea level weighs 1 .293 grams 

The average air pressure at sea level = 1033 grams per square centimeter 

METRIC AND ENGLISH EQUIVALENTS 

1 inch = 2.54 centimeters 

1 foot = 30.48 centimeters 

1 quart (U. S. liquid) = 0.9464 liter 

1 quart (U. S. dry) = 1.101 liters' 

1 ounce (avoirdupois) =28.35 grams 

1 pound (avoirdupois) = 0.4536 kilogram 

1 centimeter = 0.3937 inch 

1 meter = 39.37 inches 

1 liter = 1.051 quarts (U. S. liquid) 

1 liter = 0.9081 quart (U. S. dry) 

1 kilogram = 2.205 pounds (avoirdupois) 



520 



APPENDIX 



MENSURATION RULES 



Circumference of a circle 



= diameter X 3.1416, or ir 

Y2 circumference X radius, 
diameter squared X 0.7854, or 
radius squared X 3.1416 
diameter X circumference, or 
4 X 3.1416 X square of radius 
diameter cubed X 0.5236, or 
4 / 3 of radius cubed X 3.1416 
Lateral surface of a cylinder = circumference of base X altitude 
Volume of a cylinder = area of base X altitude 



Area of a circle 



Surface of a sphere 
Volume of a sphere 



GLOSSARY 

TERMS DEFINED AS USED IN THIS TEXT 

absolute humidity. — Weight of water vapor, grains per cu. ft. 

acclimatize, a-cli'ma-tiz. — Adaption of plants and animals to a climate. 

activated, ac'ti-vat"ed. — Rendered active, as activated sludge. 

aeration, a"er-a/shon. — To supply or charge with air. 

aerobic, a"er-o'bic. — Applied to organisms which live in free oxygen. 

aeroplane, a'er-o-plan. — A heavier- than-air flying machine. 

anaerobic, an-a"er-o'bic. — Said of organisms which thrive without free 

oxygen, 
anthracite, an'thra-sit. — Coal containing but little volatile matter, 
antiseptic, an"ti-sSp'tic. — That which prevents the growth of organisms, 
antitoxine, an "ti-t5x'in . — A substance which neutralizes toxines. 
Appalachian, ap "a-lach'i-an . — Mountain range in eastern United States, 
apparatus, ap"a-ra/tus. — Appliances and materials used in performing 

experiments, 
aqua ammonia, a'kwa a-mo'ni-a. — Ammonia dissolved in water, 
aqueduct, ak'wl-dukt. — A conduit for conveying water. 
Archimedes, ar "ki-me'dez . — Greek mathematician, 287-212 B.C. 
artesian, ar-te'zhan. — Deep well, usually flowing. First found in Artois, 

France, 
artificial, ar"ti-ffeh'al. — Produced by art, not by nature, 
assimilate, a-slm'i-lat. — -To transform food into protoplasm, 
atmosphere, at'mos-fer. — All the gases surrounding the solid earth, 
attenuate, at-ten'yu-at. — To weaken, especially in virulence, 
automatic, a "to-mat 'ic. — Self -moving, self -regulating, 
automobile, a-to-mo'bll. — Self-propelling vehicle, 
axle, aks'l. — A support upon which a wheel turns, 
bacillus, ba-cfl'tis (pi. bacilli). — A rod-shaped bacterium, 
barograph, bar-o-graf. — Instrument which writes continuous record of 

atmospheric pressure, 
barometer, ba-rSm'e-ter. — An instrument for measuring the atmospheric 

pressure. 
Baume', bo "ma/. — Antoine (an-tSin') Baume, a French chemist, 1728- 

1804. 
bituminous, bi-tu'mi-nus . — Coal with much volatile matter. Soft coal. 
Boyle, boyl. — Robert Boyle, English physicist and chemist, 1627-1691. 
buoyancy, boi'an-si. — Power or tendency to keep afloat (noun), 
buoyant, boi'ant. — Tendency to float (adjective), 
calorie, kal'o-re. — a heat unit. 

521 



522 GLOSSARY 

calorific, kal"o-rif'ik. — Heat producing. 

calorimeter, kal"o-rim'e-ter. — An apparatus for measuring heat. 

calorimetry, kal"o-rim'e-try. — Process of measuring heat. 

camphor, cam/for. — A fragrant, gum-like compound. 

capillarity, cap'11-lar'i-ty. — Force or process by which water rises through 
soil. 

capita, cap'i-ta. — Per capita (Latin) meaning per head or for each person. 

carbohydrate, kar"bo-hy'drat. — A compound composed of carbon, hy- 
drogen and oxygen. 

carbureter, kar"bu-ret'er. — 1. A device for introducing hydrocarbons 
into water gas. 2. That part of a gasoline lamp or gasoline engine 
where gasoline gas and air are mixed. 

carniverous, kar-niv'o-rus . — Applied to flesh eating animals. 

cellulose, sel'yu-los. — A material composing the cell-walls of plant struc- 
ture. 

Celsius, sel'si-us. — A Swedish astronomer, 1701-1744. 

centigrade, cen'ti-grad. — A thermometer scale (centum, Latin, meaning 
hundred) , 

centrifugal, cen-trif 'yu-gal . — Tendency to fly from the center. 

chlorine, klo'rin. — A greenish-yellow, gaseous, poisonous element. 

cirrus, cir'us. — A high cloud composed of hair-like fibers. 

clinometer, cli-nom'e-ter. — An instrument for determining altitude. 

cloud. — Water vapor condensed into visible particles floating in the air. 

coagulate, co-ag'yu-lat. — To change a substance like blood to solid form. 

coccus, cSc'iis (pi. cocci, coc'ci). — A spherical bacterium. 

conduit, con'dit. — A tube or pipe for electric wires or conducting water. 

conserving, con-serv'ing . — Preventing the waste of, as of moisture from 
the soil. 

consomme, kon"so-ma/ — A clear meat soup. 

convection, kon-vek'shon . — Transference of heat in liquids and gases by 
means of currents. 

corrode, co-rod. — To eat away gradually, to rust. 

counter-clockwise. — Turning in the direction opposite that of a clock's 
hands . 

Croton, cro'ton. — A river northeast of New York City. 

culture, cul'tur, or cul'chur. — 1. A growth of microorganisms. 2. A 
culture medium. 

culture medium. — -Material in which microorganisms will grow. 

cumulus, cu'mu-lus. — A cloud of heap-like form with rounded top. 

cutaneous, cu-ta'ne-us. — Pertaining to the skin. 

cyclone, cy'clon. — 1. A system of winds several hundred miles in diam- 
eter, circling around a center. 2. A violent storm occurring over the 
Indian Ocean. 



GLOSSARY 523 

decay, de-ca'. — Rotting, spoiling, putrefying, disintegrating. 

denitrifying, de-m'tri-fy-ing. — Removing nitrogen from compounds. 

dew. — Water vapor condensed on cool objects as grass or the ground. 

dew-point. — The temperature at or below which dew or frost would form. 

dextrin, dSks'trin. — One of the carbohydrates. 

dextrose, deks'trSs. — Grape sugar, as found in honey. 

diagnosis, di"ag-no'sis. — The identification of a disease. 

diaphragm, di'a-fram. — A dividing partition or membrane. 

diffused, dl-fusd'. — Widely scattered, as a vapor in the air. 

diff users, di-fus'ers. — Tanks in which the sugar is extracted from beets. 

diffusion, dl-fu'zhon. — The act or process of scattering. 

digestion, di-ges'chon. — The process of changing food to a soluble and 
diffusible form. 

diphtheria, dlf-the'ri-a. — An acute infectious disease of the throat. 

disinfectant, dis"In-feVtant. — A substance which will kill bacteria. 

distillation, ctis"tl-la'shun. — Operation of separating the more volatile 
from the less volatile portion of a liquid, as petroleum, or of a solid 
as wood or coal. 

divining rod, di-vin'ing. — A forked stick by means of which one pretends 
to be able to locate underground veins of water. A rod supposed to 
possess supernatural powers. 

eccentric, ee-cen'tric. — A wheel having its axle one side of its center. 

efficiency, e-fish'en-gy. — Ratio of the useful work to the energy expended. 

effluent, €f'lu-ent. — Flowing out. That which flows forth. 

enzyme, en'zym. — A substance that induces the process of digestion. 

equatorial calms, e"kwa-to'ri-al cams. — The belt of calms near the equator. 

equivalent, e-kwiv'a-lent. — Equal in value. 

eureka, u-re'ka. — "I have found it." 

evaporate, e-vap'o-rat. — To change a liquid to a vapor at a temperature 
below boiling. 

exhalation, eks"ha-la'shon.— Breathing out. 

Fahrenheit, fa'ren-hit. — A German physicist, 1686-1736. 

fallacy, fal'a-gy. — False or unsound reasoning. 

fallowing, fal'0-ing. — To cultivate land without attempting to raise a 
crop. 

faucet, fa'cet. — A spout or tap for drawing water. 

fermentation, f er "men-ta'shon . — Chemical changes induced by the en- 
zymes of organisms. 

filament, fil'a-ment. — A thread-like body, as the filament of an electric 
light bulb. 

flagella, fla-gel'a (sing, flagellum). — The swimming organs of micro- 
organisms . 

Flligge, flug'ge. — A German scientist now living. 



524 GLOSSARY 

fluorine, floo'or-In. — A pale, greenish, gaseous, exceedingly active chem- 
ical element, 
franchise, fran'chls. — A special privilege granted by the government, 
frost. — Frozen dew; formation of dew at temperatures below freezing, 
fulcrum, ful'crum. — A support against which a lever rests or upon which 

it turns, 
fungus, fun'gus (pi. fungi). — A plant of simple structure; without green 

color, 
fusion, fu'zhon. — Melting. — Act or process of changing a solid, as ice, to 

a liquid, 
galleries, gal'er-iez. — Underground passageways, 
gaseous, gas'e-us. — Pertaining to a gas or of the nature of a gas. 
gasoline, gas'o-lm. — A colorless, volatile, inflammable distillate from 

petroleum, 
gage, gag. — An instrument for measuring pressure, as of illuminating gas, 

water or steam, 
gauze, gaz. — A woven wire fabric. Wire cloth-like, fabric used to dis- 
tribute heat evenly, 
glacial, gla'shal. — Pertaining to or caused by masses of ice. 
gluten, gloo'ten. — The sticky portion of wheat flour, 
gluttenous, glut'n-us. — The act or habit of eating to excess, 
gravity, grav'i-ty. — The pull of the earth upon all objects near it. 
green plant. — A plant which has the green pigment chlorophyll in its 

leaves and other organs, 
hail, hal. — Frozen precipitation, usually composed of alternate layers of 

snow and ice. 
heredity, he-rgd'i-ty. — The process by which qualities are transmitted to 

offspring, 
horizon, ho-ri'zon. — The line between the sky and the earth or sea. 
host, host. — The organism upon which a parasite lives, 
humidifier, hu-mld' i-fi-er. — A device for increasing the moisture of 

indoor air. 
humidity, hu-mXd' i-ty. — Moisture or dampness. Condition of air as 

regards moisture, 
humus, hu'mus. — The organic matter of the soil, usually giving it a dark 

color, 
hurricane, hur'i-ean. — A violent storm of the cyclone type occurring in 

the West Indies, 
hydrant, hy'drant. — A discharge pipe connected with a city water main 

for fire fighting, 
hydraulic, hy-dra'lle. — Pertaining to water under pressure, as hydraulic 

pressure. 



GLOSSARY 525 

hydrocarbon, hy "dro-kar'bon . — A compound composed of hydrogen and 

carbon . 
hydrochloric acid, hy"dro-klo'ri€ as'Id. — A compound of hydrogen and 

chlorine, 
hydrometer, hy-drom'e-ter. — An instrument for determining the density 

of liquids, 
hydrophyte, hy'dro-fit. — A plant which lives in water or water soaked 

ground, 
hypha, hy'fa (pi. hyphas). — The thread-like parts of a fungus, 
hypocaust, hyp'o-cast. — Basement chambers and flues used for heating 

Roman buildings. 
Imhoff, im'hof . — Inventor of a certain form of septic tank, 
immunity, l-mu'ni-ty. — Freedom from liability of a disease.- 
incandescent, in"kan-des'ent. — White or glowing from heat, 
inclemency, In-clem'en-cy. — Harsh, severe, rigorous, applied to weather 

or climate, 
infection, In-feVshon. — To be inoculated with disease organisms, 
infiltration, in"fil-tra'shon. — Passing of liquids through small openings, 
inhalation, in"ha-la'shon. — Breathing in. 
inoculate, In-oc'yu-lat. — To put disease organisms into the body of an 

animal or plant, 
inorganic, in"6r-gan'i€. — Not organic. Not formed by or pertaining to 

an organism, 
insulation, in"su-la'shon. — Surrounding a body with non-conductors, as 

of heat or electricity, 
intermittent, in'^er-mit'ent. — Interrupted. Ceasing at intervals, 
interurban, in "ter-ur'ban . — Between cities, applied to electric railroads, 
iodine, I'o-din. — A bluish-black, crystalline element, used externally as a 

medicine . 
irrigate, ir'i-gat. — To water land by artificial means, 
isolated, is'o-lat"ed. — Separated from others. In a detached place. 
Joule. — James Prescott Joule, an English physicist, 1818-1889. 
Keokuk, ke'o-kuk. — A city in Iowa on the Mississippi River, 
kerosene, ker'o-sen. — Common illuminating oil. A product of petroleum, 
kilowatt, klTo-wat. — A unit of electrical energy equal to 1000 watts. 
Kuwoshiwo, ku"ro-shi'wo. — (Formerly Kuwo-Siwo), — Japanese Current 

in the Pacific Ocean, 
lactose, lak'tos. — The sugar found in milk. 
Langley, lang'ly. — Samuel Pierpont Langley, American scientist, 1834- 

1906. 
leaching, lech'ing. — 1. Dissolving mineral salts out of the soil. 2. Soaking 

of sewage into the soil, 
lever, le'ver or lev'er. — One of the simple machines. A stiff, rigid bar. 



526 GLOSSARY 

levulose, leVu-los. — The sugar found in fruits. 

life process. — A process necessary to life. 

lightning, lit'ning. — The flash of an electric discharge to or from a cloud. 

liquefy, Hk'we-fy. — To convert into or to become a liquid. 

loom, loom. — A flexible insulating tube used as a conduit for electric wires. 

Los Angeles, 15s an'ge-lez. — A city in southern California. 

luminous, lu'mi-nus. — Giving off light. 

luxurious, lug-zhu'ri-us. — Pertaining to indulgence in pleasure of the 

senses which are unnecessary for health and comfort, 
maltose, mol'tos or malt'os. — A hard, white, crystalline sugar formed by 

the action of malt on starch, 
manometer, ma-nom'e-ter. — An instrument for measuring pressure, 
maximum, max'i-mum. — Highest. The maximum thermometer indicates 

the highest temperature, 
mean, men. — Average. The mean temperature is the average temperature, 
mechanical advantage. — Advantage obtained by using a mechanical 

device, 
mesophyte, mes'o-flt. — A plant which requires a medium amount of 

moisture . 
metabolism, me-tab'o-hzm or me-tab'o-lism. — Total process of obtaining 

nourishment from food, 
microorganism, mI' / €ro-6r'gan-Ism.— An organism that can be seen only 

by use of the microscope, 
microscopic, mi"€ro-S€op'ic. — Seen only by the aid of a microscope, 
minimum, mm'i-mum. — Least, lowest. The minimum thermometer indi- 
cates the lowest temperature, 
molecule, mol'e-cul. — The smallest particle of matter that can exist as 

such, 
monsoons, m5n-sdons'. — Winds along the coast, blowing toward the land 

in summer and toward the sea in winter, 
mycelium, my-ce'li-um. — The plant body of a fungus, 
naphtha, naf'tha. — A volatile distillate from petroleum, 
neutralize, nu'tral-iz. — To destroy the power of, as acids neutralize 

alkalies . 
Newcomen, nu-com'en. — Thomas Newcomen, an English inventor, 1663- 

1729. 
non-green plants. — Plants which lack chlorophyll and therefore are not 

green . 
non-luminous, nSn-lu'mi-nus . — Not giving off light, 
nutation, nu-ta/shon. — A revolving motion, giving rise to a nodding 

motion, 
nutrition, nu-trlsh'6n. — The process by which growth is promoted and 

waste repaired in living organisms. 



GLOSSARY 527 

oleomargarine, o "le-o-mar'ga-rin (not mar'jer-en) . — A substitute for 

butter, 
olla, ol-a (Spanish). — A porous, earthen water jar or container, 
organic, or-gan'ic. — 1. Formed by or pertaining to an organism. 2. A 

chemical compound having carbon for its chief constituent, 
organism, or'gan-ism. — A living being having different organs performing 

special functions, 
oscillating, 6s'i-lat"ing. — Swinging back and forth on its axis, 
paraffin, par'a-fin. — A translucent, waxy, solid substance derived from 

petroleum, 
parasite, par'a-sit. — An organism that lives upon or within the body of 

another. 
Pasteur, pas"tur'. — Louis Pasteur, a celebrated French chemist and 

bacteriologist, 1822-1895. 
pasteurization, pas "tur-i-za/shon . — Killing active organisms by heat, 
pathogenic, path "o-gen'ic . — Disease causing. 

percolation, per "co-la/shon . — Passing slowly through small openings, 
perforated, per'fo-rat"ed. — Pierced with small holes, 
pinion, pin 'yon. — A small toothed wheel driving or driven by a larger 

cog-wheel, 
pitman, pit 'man. — A rod connecting a moving lever with a rotating wheel, 
platinum, plat'i-num. — A valuable, steel-gray, heavy, malleable metallic 

element, 
plenum, ple'num. — Applied to space full of matter, as plenum system of 

ventilation, 
pneumatic, nu-mat'ic. — Pertaining to or containing compressed air. 
Ponce de Leon, pon'the de le'on. — Juan Ponce de Leon, a Spanish ex- 
plorer, 1460-1521. 
porcelain, purg'lin, or por'ce-lan. — A translucent earthenware, usually 

glazed, 
precipitation, pre-cip"i-ta/shon. — Water from the atmosphere falling to 

or toward the earth, 
propulsion, pro-pul'shon. — Pushing; operation of propelling, 
protein, pro'te-m. — One of the three food principles, 
protractor, pro-trae'tor. — An instrument for measuring angles, 
radiation, ra "di-a'shon . — The giving off of heat to or through space, 
range, rang. — 1. A stove with one side as a front. 2. Difference between 

the highest and the lowest, as the range of temperature, 
relative humidity. — The humidity expressed in per cent, of saturation, 
reservoir, rez'er-vwor or reVer-vwor. — A huge tank or receptacle for 

storing water, 
residue, res'i-du. — The portion remaining after part is removed. 



528 GLOSSARY 

revolution, reV'o-lu'shon. — Complete circuit made by a body around a 

center. 
Roquefort, rok"for' or rok'fort. — A commune in France famed for its 

goats and cheese . 
rotary, ro'ta-ry. — Turning around completely on its axis, 
sanitary, san'i-ta-ry. — Relating to the preservation of health, 
saturation, sach "u-ra/shon . — State of being filled with (water) vapor, 
sedentary, sed'en-ta-ry. — Pertaining to inactivity, as a sedentary life, 
semi-transparent, sem"i-trans-par / ent. — Partly admitting, of the passage 

of light, 
septic, sSp/tlc. — Productive of putrefaction, rotting or decaying, 
serum, se'rum. — Blood with the corpuscles removed. A part of the blood, 
sewage, su'ag. — Waste matter carried off in sewers, 
shower, show'er. — A brief fall of rain, sometimes of hail or snow. 
Sierra Nevada, si-er'a ne-va'da. — A mountain range in eastern California, 
silicon, sfl'i-kon. — One of the chemical elements found in sand, 
siphon, si' fon. — A bent tube through which liquid flows, 
sleet, slet. — Frozen or partly frozen rain, 
sludge, sltidg. — Soft, muddy, pasty, refuse which forms in the bottom of a 

septic tank, 
snow. — Falling water vapor condensed at a temperature below freezing, 
solstice, sol'stic. — Date upon which the sun seems to turn back north in 

the winter, December 22, or back south in the summer, June 21. 
specific heat, spe-sif'Ik. — Heat required to raise 1 gram of a substance 1°C. 
spore, spor. — A reproductive cell in higher fungi. A resting cell in bacteria, 
squall cloud, skwal. — A low, ragged, tumbling cloud often seen with the 

wind gust in front of a thunderstorm, 
sterile, ster'il. — Free from microorganisms, 
sterilization, steV'il-I-za/shon. — Act of making sterile, 
stratus, stra'tus. — A flat layer cloud of rather uniform thickness, 
strata, stra'ta (sing, stratum). — Layers, as of rock in the earth's crust, 
substratum, sub-stra/tum. — Material through which the hyphas of a 

fungus grow, 
sucrose, su/kros. — One of the sugars, as cane sugar, beet sugar, maple 

sugar, 
susceptible, siis-cep'ti-ble. — Opposite of immune; liability to disease, 
thermograph, ther'mo-graf. — An instrument for writing a continuous 

record of temperature, 
thermostat, ther'mo-stat. — A device for automatically regulating tem- 
perature, 
threshing, thresh'ing. — Separating grain or seed from straw or stalks, 
thunderstorm, thun'der-storm. — A shower accompanied by thunder and 

Ughtning. 



GLOSSARY 529 

tornado, tor-na/do. — A violent, whirling, twisting wind a few hundred 
yards or less in diameter, usually with a hanging funnel cloud at its 
core. 

toxine, toks'm. — A poison, often of bacterial origin. 

treadle, tred'l. — -A lever operated by the foot to run a machine, as a 
sewing machine. 

tungsten, tung'sten. — A steel-gray, heavy, metallic metal, used for lamp 
filaments . 

turbine, tur'bm or tur'bi'n. — One form of water wheel. 

typhoon, ty-foon'. — A violent cyclonic storm occurring over the China 
seas. 

vaccinate, vac'ci-nat. — To treat with a vaccine. 

vaccine, vae'cJLn. — A substance which induces immunity in an organism. 

vacuum, vae'yu-um. — Space without matter, especially space devoid of 
air. 

vaporize, va'por-iz. — To change into gaseous form. 

vernier, ver'ni-er. — A sliding scale on a barometer for measuring to very- 
small divisions. 

vibrating, vi'brat-ing. — Moving back and forth in a straight fine or the 
arc of a circle. 

virulence, vlr'u-lenc. — The disease producing property of an organism. 

virus, vi'rus. — The substance used in vaccination. 

vitality, vi-taTi-ty. — Life; power; surplus energy. 

vitiated, vlsh'i-at "ed . — Polluted; impure. 

volatile, v51'a-tfl. — Easily evaporated. 

waterspout. — A tornado occurring over water. 

Welsbach, wels'bac. — Carl Auer Freiherr Welsbach, an Austrian scientist, 
1858- 

westerlies . — The belt or zone of winds blowing from the west in both tem- 
perate zones. 

xerophyte, ze'ro-fite. — A plant which thrives in dry soil and dry air. 

yucca, yue'a. — Lily-like plant, a native of southwestern United States 
and Mexico. 



INDEX 



(All References Are to Pages.) 



Absolute humidity, denned, 362. 
Activated sludge plant, 448. 
Aerobic bacteria, 287. 
Air, pure, composition, 233; com- 

plemental, tidal and reserve, 

237; pressure of, 138; vitiated, 

theories about, 234; weight of, 

137. 
Airblast on stoves and furnaces, 

90. 
Ammonia, properties of, 370; as 

a refrigerant, 371. 
Anerobic bacteria, 287. 
Antenaria, 268. 

Anthracite coal, how it burns, 86. 
Anthrax, 299;. symptoms of, 300; 

prevention and cure, 301-304. 
Antiseptics, 291. 
Aqueducts, 404; of Segovia, Spain, 

405. 
Archimedes' principle, 106. 
Artesian wells, 401. 
Aspergillus, 266. 

Babcock, butter-fat test, 340-341. 

Baccilli, 278; anthraxis, 301. 

Bacteria, 279; where found, 279; 
favorable conditions for, 289; 
food for, 289; temperature re- 
quired, 289. 

Bacteriology, 276. 

Balances, beam, 471; spring, 472. 

Ball bearings, 480. 

Barograph, 144. 

Barometer, construction of, 140; 
correcting for temperature, 141; 
temperature correction table, 
145 ; correcting for altitude, 
142 ; altitude correction table, 
146-147. 

Bath-rooms, in 1875, 431; modern, 
432. 

Baths, Roman, 428. 

Beam balances, 471. 



531 



Beaume's hydrometer, 27. 

Bibb or faucet, 430. 

Bituminous coal, how it burns, 
86. 

Body-temperature, how controlled, 
239. 

Boiling, definition of, 15. 

Boiling-point, definition, 19 ; of 
alcohol, 20. 

Boyle's law, 391. 

Bread and butter, 335. 

Breathing, earth's, 390; effect of 
animals on composition of air, 
234. 

Brine, why used in ice plant, 374. 

British thermal unit, defined, 98. 

Buoyancy, 105. 

Burning fluid, 6. 

Burning point, defined, 6. 

Butter, 342; renovated, 342, proc- 
ess, 342. 

Butterine, 343; test for, 345. 

Calorie, lesser and greater, 98. 
Candle, 2; how it burns, 2. 
Canning food, 392; domestic, 293; 

factory, 294. 
Carbohydrates, 329; test for, 329. 
Carbon, 74; carbon cycle, 326. 
Carbureter of gas machine, 35. 
Center draft burners, 8. 
Centigrade thermometers, 15. 
Central Square water works, 416. 
Centrifugal force, 465. 
Cereal foods, 349. 
Cesspool, 439. 

Chain stitch sewing machine, 456. 
Chaldeans and the weather, 133. 
Charles' law, 104. 
Cheese, 346; filled, 347. 
Chemical energy, 81. 
Chemical union, 72. 
Chimnev, draft of, 108; invention 

of, 103. 
Classification of plants, 263. 



532 



INDEX 



Climate, definition of, 216; accept- 
ing one, 229; and animal life, 
218; change of beneficial, 231; 
factors of, 219-224; and health, 
225; ideal, 225; indoor, 230; 
and man, 218; and plant life, 
216; and weather, 216. 

Climatic areas, 226-229. 

Clinometer, 209. 

Cloud forms, 168-174. 

Clouds, how formed, 175. 

Coal, wastes in mining, 99; how 
long supply will last, 100; fields 
of, 101; annual production, 100; 
development of, supply, 99; gas, 
95. 

Cocci, 278. 

Coking chamber, 90. 

Cold storage, 377. 

Colds, 317. 

Complemental air, 237. 

Compounds, 72. 

Compression in gas engine, 513. 

Conductors, of heat, 131. 

Conduits, electric, 48. 

Contact filters, 445. 

Convection currents, cause of, 104; 
about a heated stove, 109. 

Cook stoves, early, 127; modern, 
128. 

Cooking devices, development of, 
125. 

Corn, as food, 351; flakes, 352; 
starch, 352. 

Cost of work, by steam engine, 
486 ; by horse, 487 ; by man, 489. 

Cotton-seed oil, 349. 

Cowpox, 306. 

Cream separation, shallow set- 
ting, 463; deep setting, 464; 
water dilution, 464. 

Cream separator, 463; centrifugal, 
466. 

Cropping, effect on soil nitrogen, 
286, 

Crowd poisoning, 234. 

Cugnot's steam carriage, 509. 

Cumulus clouds, 174. 

Dairy products, 339. 
Decay, 278 and 288. 
Deep setting of milk, 464. 
Deep wells, 400; for city supply, 
421. 



Dew point, 166; defined, 362. 

Dew or frost, 167. 

Diet, 322. 

Diffused light, natural, 51; arti- 
ficial, 54. 

Diphtheria, 308; toxin and anti- 
toxin, 310; effect of antitoxin 
treatment, 312; cause and symp- 
toms, 308. 

Direct radiation, 252. 

Disease, theories of, 298. 

Disinfectants, 291. 

Distillation, of alcohol, 21; defi- 
nition, of, 22; of wood, 83; of 
coal, 87. 

Distribution of light, 61. 

Drains, 433. 

Drapery and dust, 256. 

Dry air, evil effects of, 244; and 
high temperature, 245. 

Dust, house, 255; dead dust, 255; 
live dust, 255. 

Earth's breathing, 390. 

Eccentric, 507. 

Efficiency, of machines, 481; of 
motors, 485. 

Electric current, heating effects of, 
46, 

Electric energy, transmission of, 
498. 

Electric lamps, sizes of, 63. 

Electric, wiring, 48; lighting, 45. 

Elements, chemical, 71. 

Elliptical laws, 196. 

Energy, definition of, 81; and liv- 
ing beings, 260; and foods, 326; 
and machines and motors, 484; 
source of, 496. 

Evaporation, experiments, 10; 
laws of, 12; definition of, 16; 
map of annual, 162; to secure 
proper humidity, 246. 

Expansion tank, hot water sys- 
tem, 116. 

Explosive mixture, of hydrogen 
and air, 80; of gasoline vapor 
and air, 96. 

Factory, coming of, 453. 
Fahrenheit thermometer, 15. 
Fall plowing, 395. 
Family of plant life, 263. 
Fats, 329. 



INDEX 



533 



Faucet or bibb, 430. 

Filters, contact, 445; sprinkling, 
447. 

Fire, discovery of, 1; importance 
of, 66; hydrant, 423. 

Fireless cookers, 130. 

Fire-place, 67. 

Flashing-point, definition, 4 and 
30; of paraffin, 4; of gasoline 
and. kerosene, 29. 

Float valve, 437. 

Fluctuating indoor temperature, 
241. 

Flushing tank, 436. 

Fog, ground, 168. 

Food, importance of studying, 322 ; 
definition of, 327; classes of, 
327 ; principles, 328 ; the use of, 
323; chemical elements of, 324; 
energy of, 324; composition and 
calorific values of, 333 ; how 
much required, 334; heat value 
of food principles, 335; amount 
needed per day, 336; processing 
of, 338. 

Force, definition of, 473; units of, 
473. 

Force-pump, 408. 

Four-cycle gas engine, 512. 

Franchise, 414. 

Franklin's stove, 70. 

Fresh air needed, calculation of, 
235. 

Friction, definition of, 479 ; and 
machines, 481; sometimes use- 
ful, 482. 

Frost, protection from, 157-160; 
maps of dates, 162. 

Fuel, elements, 73; heat values of, 
98. 

Furnaces, setting of, 110; to be 
successful, 114. 

Galileo, 137. 

Gas, burners, 45; and electric 
lights, relative cost compared, 
62; pressure measured, 44. 

Gas meter, 40; exercise, 41; read- 
ing of, 43 ; recording mechanism 
of, 44. 

Gaseous fuels, 94; coal gas, 95; 
water gas, 95; gasoline gas, 96. 

Gasoline, how obtained, 25 ; grades 
of, 27; gasoline gas machines, 



34; commercial importance of, 
36; from natural gas, 37; from 
residue or motor spirits, 37; 
used as a fuel, 96. 

General circulation of atmosphere, 
203. 

General storm, study of, 189; of 
December 4 to 6, 1906, 190- 
194. 

Generator for water gas, 96. 

Genus of plants, 262. 

Glaze, ice storm, 178. 

Glucose, 353; preparation of, 354. 

Gluten, 350. 

Graham flour, 350. 

Gravitation, 470. 

Gravity, 470. 

Greeks and the weather, 133. 

Grippe or influenza, 316. 

Ground air, movements of, 388. 

Ground fog, 168. 

Ground water, 381-383; and river 
water, 387. 

Guericke, Otto von, invented air- 
pump, 137. 

Hail, how formed, 185; soft, 178. 

Hay culture, study of, 276; life 
history of, 277. 

Heat, measurement of, 97; and 
temperature, distinction be- 
tween, 97; quantity, units of, 
98. 

Heat of vaporization, 119. 

Henry's law, 412. 

Highs, changes which accompany, 
198; in southern hemisphere, 
197-198. 

Hindus and the weather, 133. 

Hippocrates, 298. 

Horse-power-hour, equals 640 calo- 
ries, 486 ; cost of by using steam 
engine, gasoline engine, horse, 
and man power, 488. 

Hosts, 297. 

Hot water system of heating, 115; 
contrasted with steam, 120; ad- 
vantages of, 116; essential fea- 
tures of, 116. 

House, dust, 255; heating, 101. 

Humidifier, 247. 

Humidifying school-rooms, 248. 

Humidity, and ventilation, 239; 



534 



INDEX 



importance of, 242; too low in- 
doors, 243. 

Humus, and soil moisture, 395. 

Hydrocarbons, 80. 

Hydro-electric plants, 498. 

Hydrogen, preparation of and 
properties of, 78. 

Hydrometer, Beaume's, 27. 

Hydrophytes, 393. 

Hygrometer, 165. 

Ice cream,, how frozen, 375. 

Ice factory, 369. 

Ice storm, glaze, 178. 

Ideal indoor temperature, 240. 

Illuminating gas, 39. 

Imhoff tank, 442. 

Immunity, natural and acquired, 
303. 

Incandescent lamp, carbon, 46; 
tungsten, 47; nitrogen filled, 47. 

Indirect lighting, 58. 

Indirect radiation, 251. 

Indoor climate, 230. 

Indoor ideal temperature, 240. 

Infiltration galleries, 387. 

Influenza or grippe, 316. 

Inhalation, earth's, 390. 

Insensible heat, factors of, 117; 
required to evaporate water, 118. 

Internal combustion engines, 508; 
and automobiles, 508; and aero- 
planes, 510. 

Invisible water supply, 381. 

Jenner, Edward, 305. 

Keokuk power plant, 493. 

Kerosene, lamp, 5 ; burning with- 
out burner, 7; vapor which 
burns, 8; use in kindling fire, 
31; cheap kerosene, danger of, 
32. 

Kilowatt-hour meter, 62; reading 
of, 64. 

Kindling temperature, 77. 

Koch, Robert, 276. 

Lamp, primitive, 1 ; Greek and 

Roman, 2. 
Lamrlev's aeroplane, 509. 
Lard. 349. 

Lavoisier's explanation of fire, 71. 
Length of day, effect of, 213. 



Lift-pump, 408. 

Lighting, natural and artificial, 

49; importance of studying, 49; 

direct and diffused, 50. 
Lightning, 184. 
Liquid fuels, burning of, 93. 
Living in the open air, 232. 
Local storms, 178. 
Lock stitch sewing machines, 460. 
Low, in southern hemisphere, 197- 

198. 
Lows, unusual paths, 201-202. 
Luminous flames, 85. 

Machines, 476; simple and com- 
pound, 479; law of, 480; and 
friction, 481. 

Manufactured ice, 368 ; purity and 
cost of, 374. 

Mass, meaning of, 469; units of, 
469. 

Meat foods, 347; preserving of, 
347; inspection of, 348. 

Mechanical advantage, 477; nu- 
merical expression of, 478. 

Mechanical stokers, 93. 

Mesophytes, 394. 

Metabolism, and temperature, 240 ; 
defined, 239. 

Microorganism^, 260; and food, 
260. 

Migration of the sun, 206. 

Milk, 339; fat in, 339. 

Miraflores water purification 
plant, 417. 

Mixer, of gasoline gas machines, 
36. 

Mixtures and compounds, 73. 

Moisture and the industries, 165. 

Molds, growing them, 264 ; collect- 
ing them, 265; digestion by, 
265; spores of, 266; identifying, 
267 ; favorable conditions for 
growth, 267-269; effect on food, 
269. 

Motors, 483; animal and mechan- 
ical, 484; efficiency of, 484. 

Motor spirits, 37. 

"Nature, abhorence of a vacuum," 

138. 
New York City water system, 417. 
Newcomen air-steam engine, 501. 
Night cooling, 157. 



INDEX 



535 



Nitrifying, bacteria, 282. 
Nitrogen-filled lamps, 47. 
Nitrogen fixing bacteria, 283. 
Nodule bacteria, 284. 
Non-conductors of heat, 131. 
Non-luminous flames, 85-130. 
Nutation motion in water meter, 
425. 

Oil fields of U. S., 38. 

Oils, inspection of, 28; when dan- 
gerous, 32. 

Oleomargarine, 343; tests for, 345. 

Open-air living and sleeping, 232. 

Open grate, 124. 

Oxidation, slow, 77 

Oxids, defined, 77. 

Oxygen, and combustion, 5 ; prep- 
aration and properties, 75. 

Paraffin, flashing and burning 
points, 4. 

Parasites, 297; and saprophytes, 
261. 

Passing storm, summary, 196. 

Pasteurization, 296-297. 

Pasteur, Louis, 276. 

Paths of highs and lows, U. S., 
199. 

Pencillium, 266. 

Petroleum, how obtained, 23 : dis- 
tillation of, 24 ; products of, 25 ; 
rise of industry, 38; how long 
will supply* last, 38; annual 
production of, 39. 

Pioneer's tools, 452. 

Plant relationships, 262. 

Plenum system of ventilation and 
heating, 253. 

Plumbing, 427 ; system for city 
dwelling. 419: system for coun- 
try dwelling. 410. 

Pneumatic tank system, 409. 

Pneumococci, 314. 

Pneumonia, 314. 

Pork and beans, as food, 335. 

Porosity, of soils, 383. 

Potter, Humphrey, invention by, 
502. 

Power, activity or rate of work, 
475. 

Power house, farm, 454. 

Pressure gage, 122; water, 423. 



Proteins, test for, 330; amount 

necessary, 332. 
Psychrometer, sling, 163-165. 
Public health, 321. 
Pump, suction, 407; lift, 408; 

force, 409. 
Pure air, composition of, 233. 
Putrifaction, 288. 
Pyroligneous acid, 83. 

Radiation, checking of, 158. 

Rain, how produced, 176. 

Rain -gage, 148. 

Rainfall map, 217. 

Range, coal, 129; gas, 130. 

Reducing valve, 122. 

Reflector, for cooking, 126. 

Refrigeration and transportation, 
380. 

Refrigerator, 126; uses of, 358; 
styles of, 359; why dry, 364; 
effect on foods, 365; tempera- 
ture obtained, 359 ; exercise, 
study of, 361; care of, 368;' 
mechanical for home, 367. 

Registers, placing of, 112. 

Regulator, air for gas stove, 130. 

Relative humidity, testing, 246; 
defined, 362. 

Reserve air, in lungs, 237. 

Residual air, in lungs, 237. 

Risers or stacks for furnace heat- 
ing, 112. 

River-water and ground-water, 
387. 

Roman, baths, 428; hypocaust, 
102. 

Rotting, 288. 

Safety valve, 123. 

Saprophytes and parasites, 261. 

Saturation, defined, 362. 

Season, lag of, 157. 

Semi-indirect light, 60. 

Sensible heat, factors of, 117. 

Septic tank, 440. 

Sewage, 437. 

Sewing machine, classes of, 456. 

Shallow setting of milk, 464. 

Shallow wells, 413. 

Shelter, for weather instruments, 

153. 
Showers, to foresee, 179; paths of, 

179. F 



536 



INDEX 



Sink-holes, 438. 

Siphon, 435. 

Sleeping, porch, 231: in open air, 
232. 

Sleet, 178. 

Slow oxidation, 325. 

Sludge, 444; activated, 448. 

Smallpox, 304; origin of vaccina- 
tion for, 304; cause of, 305; ef- 
fectiveness of vaccination, 306; 
reaction against vaccination 
and its effect, 307. 

Smoke, cause of, 88; evil effects 
of, 89; how prevented, 89. 

Snow, 177; measurement of, 149. 

Soapstone, in tireless cookers, 132. 

Soil moisture, conservation of, 
395; increasing, 395. 

Soil, nature of, 280; bacteria and 
carbon, 281; and nitrogen, 281. 

Soil-air, diffusion of, 392. 

Soil-pipe, 434. 

Solid fuels, composition of, 88. 

Solstice, summer and winter, 211. 

Species, of plants, 262. 

Specific heat, denned, 98. 

Spirilla, 278. 

Spores, bacteria, 279. 

Spring balances, 472. 

Stacks or risers, 112. 

Steam engine, 499 ; earliest, 500 ; 
source of power in, 501; modern, 
506. 

Steam heating, 119; contrasted 
with hot water heating, 120; 
safety devices, 122. 

Steelyards, 472. 

Sterilization, 296. 

Strata, earth's, 383. 

Sucking, definition of, 259. 

Suction, definition of, 259. 

Suction-pump, 407. 

Suction system of ventilation, 254. 

Sugar, cane, 355; beet, 356; re- 
fining of, 357. 

Summary of sewage disposal, 449. 

Summer solstice, 211. 

Sun's altitude, measurement of, 
200; effect on heating power, 
210. 

Sun's migration, effect of, 206. 

Sun's shadow, measurement of, 
210. 

Sunshine maps, 223. 



Superheater for water gas, 96. 
Surface wells, 400. 

Temperature, meaning of, 12; 

points in Nature 14; lag of 

daily, 156; maps of the U. S., 

220-221; fluctuating, desirable, 

241. 
Thermograph, 152. 
Thermometer, principle of, 13; 

Fahrenheit, 15; centigrade, 15; 

maximum, 150; minimum, 151. 
Thunder, 185. 
Thunderstorm, 181-183; map of, 

184. 
Tidal air, 237. 
Tools of the pioneer, 452. 
Tornado, 186-188, 
Torricelli's experiment, 138-139. 
Toxins, 297. 
Transportation and refrigeration, 

380. 
Traps, 435; siphoning of, 435; in 

a steam heating system, 122. 
Tuberculosis, 317; danger of, 319; 

curable, 320. 
Tungsten lamp, 47. 
Typhoid fever, 315; carriers, 316. 

Underfeed furnaces, 92. 
Under-ground streams, 397. 
Unusual weather, cause of, 201. 

Vaccination, for anthrax, 304; for 
smallpox, 306. 

Vacuum cleaning, 257. 

Van Leeuwenhoek, Anthony, 276. 

Vaporize, definition of, 16. 

Vapors, of fat, 3. 

Vein of water, 398. 

Ventilation, summary of, 248 ; sys- 
tems of, 250; in colonial days, 
250; of dwellings, 251; ventila- 
tion and humidity, 239 ; theories 
of, 234-238; need of, 233. 

Visible water supply, 381. 

Vitiated air, theories about, 234. 

Wagon scales, 472. 

Water, gas, 95 ; carbureted, 96 ; 
gage, 124; table or plane, 384; 
lift, 422; meter, 424; reliable, 
425; reading of, 426; front and 



INDEX 



537 



back, 429 ; dilution of milk, 464 ; 
motors, 491-492. 

Water power, amount and distri- 
bution, 498. 

Watt-hour, 62. 

Watt-hour-meter, 63. 

Watt's engine, 503; double acting, 
506. 

Weather, the, 133; record, non- 
instrumental, 135; record, in- 
strumental, 154; chart, 200. 

Weight and force compared, 473. 

Well water, 382. 

Wells, surface and deep, 400; deep, 
421; shallow wells dangerous, 
412; artesian, 400. 

Whale oil lamps, 5. 

Wheat, flour, 350; entire, 350; 
shredded, 351. 

Wind, and personal comfort, 156; 



and frost, 161; wind system of 

the earth, 205; map, 222. 
Winter solstice, 211. 
Witching for water, 399. 
Wood, burning of, 82; distillation 

of, 83. 
Work, 474; units of, 474; time no 

factor in work, 474; and heat, 

483. 

Xerophytes, 394. 

Yeasts, 269; prevalence of, 269; 
growing yeasts, produce carbon 
dioxid, 270; produce alcohol, 
271; and fermentation. 271; and 
alcoholic liquors, 272; and 
bread, 273; and preservation of 
food, 274; wild and cultivated, 
274. 



